Films having enhanced sealing characteristics and packages containing same

ABSTRACT

Films containing a sealant layer composition comprising: (1) polyethylene homopolymer, and ethylene/alpha-olefin copolymer, ethylene vinyl acetate copolymer, and ethylene/acrylate copolymer; and (2) elastomer, plastomer, ionomer, and carboxyl-modified polyethylene; when sealed to another outer film layer comprising at least one member selected from the group consisting of ionomer, ethylene/acid copolymer, ethylene/vinyl acetate copolymer and ethylene/acrylate copolymer, have been discovered to provide a seal strength comparable to an ionomer to ionomer seal.

FIELD OF THE INVENTION

The present invention relates generally to films, both monolayer filmsand multilayer films, and particularly to packaging films. The presentinvention also relates to packages, especially packages having one ormore seals, as well as packaged products. The present invention isparticularly related to films suitable for sealing, especially heatsealing.

BACKGROUND OF THE INVENTION

Multilayer films having one or more tie layers containing a blend of anethylene/alpha-olefin copolymer and a plastomer and/or an elastomer, areknown. Such tie layers are internal film layers which those of skill inthe art recognize as being compatible with other compositions, i.e.,suitable for direct adhesion to, for example, ionomers and polyethylenehomopolymers and copolymers.

Multilayer films with one or more surface layers containing a blend ofan ethylene/alpha-olefin copolymer and a plastomer, and/or an elastomer,are also known. However, such films have been used in a manner in whichthe outer blend-containing sealing layer is sealed to itself, and thepackage is a high strength, heat-resistant structure which has been usedas dunnage bags (which contain air, and are used to stabilize loadsduring shipping, these films comprising an ethylene/alpha-olefincopolymer having a density of about 0.916 or greater) and for use in thepackaging of water softener, i.e., salt pellets.

Ionomers such as metal-neutralized copolymers of an olefin and acarboxylic acid are also known for use in an outer film layer. Ionomersare advantageous in the (outer) sealing layer of a film because theymelt at relatively low temperature and produce a relatively strong heatseal. However, ionomers are expensive relative to other polymerstypically used in packaging films.

Since ionomer-containing resins are expensive, it would be desirable touse less ionomer, or no ionomer, without sacrificing the advantageousproperties provided by ionomers, such as low seal initiationtemperature, relatively high seal strength, relatively high hot tackstrength, suitability for seals used in cook-in conditions, acceptablefor food contact, etc. Furthermore, it would also be desirable toprovide a film having a relatively thick layer or layers which undergomelt flow during sealing, so that the resulting seal is capable ofsealing through or around surface imperfections, or contamination suchas dust, fat, water, the product being packaged, e.g. food, such asmeat. Of course, it would also be desirable to provide at low cost thisrelatively thick region capable of melt flow during sealing, i.e., usingcompositions which are inexpensive, especially compositions lessexpensive than ionomer.

SUMMARY OF THE INVENTION

The present invention is the result of a discovery that a polymercomposition which includes two or more different polymers, in an outersealant layer and/or a seal-assist layer in packaging films, provide thefilms with highly desirable sealing characteristics, including one ormore of the following: (a) low seal initiation temperature, (b) highseal strength, (c) high hot tack strength, (d) suitability for sealsused under cook-in conditions, and (e) acceptable outer layer for use indirect contact with food. Moreover, it is most significant that thesecompositions rival the sealing performance of ionomer compositions whichcurrently set the standard of commercial performance with respect tosealing, while being substantially less expensive than ionomercompositions. Thus, the present invention permits the use of lessionomer, or no ionomer, without sacrificing the advantageous sealproperties provided by ionomers.

Furthermore, the composition of the present invention can be used toprovide a film having a relatively thick layer or layers which undergomelt flow during sealing, so that the film is capable of sealing throughcontamination such as dust, fat, water, the product being packaged,especially food, such as meat, as well as sealing around surfaceimperfections. Providing such a relatively thick surface of ionomer isoften so expensive that it is not commercially cost-prohibitive. Thus,the present invention enables the use of relatively thick sealinglayers, with their respective advantages -as set forth above, incommercial applications which previously have been cost-prohibitive.

As a first aspect, the present invention pertains to a packagecomprising a seal of a first outer film layer to a second outer filmlayer. The first outer film layer comprises a composition. Thecomposition comprises a first component and a second component. Thefirst component comprises at least one member selected from the groupconsisting of polyethylene homopolymer, and ethylene/alpha-olefincopolymer. The second component comprises at least one member selectedfrom the group consisting of elastomer, plastomer, and carboxyl-modifiedpolyethylene. The second outer film layer comprises at least one memberselected from the group consisting of ionomer, ethylene/acid copolymer,and carboxyl-modified polyethylene.

Preferably, the first outer film layer comprises from about 1 to 99percent of the total thickness of the film in which it is present; morepreferably, from about 3 to 75 percent; still more preferably, fromabout 5 to 40 percent; and yet still more preferably, from about 7 to 25percent.

Preferably, the first outer film layer has a seal initiation temperatureof from about 175° F. to 300° F.; more preferably, from about 175° F. to250° F.; and, still more preferably, from about 175° F. to 225° F.

Preferably, the composition comprising the first component and thesecond component comprises from about 5 to 95 weight percent of thefirst component with from about 95 to 5 weight percent of the secondcomponent; more preferably, from about 50 to 90 weight percent of thefirst component with from about 10 to 50 weight percent of the secondcomponent; still more preferably, from about 80 to 30 weight percent ofthe first component with from about 20 to 70 weight percent of thesecond component; and yet still more preferably, from about 70 to 50weight percent of the first component with from about 30 to 50 weightpercent of the second component.

As a second aspect, the present invention pertains to a packagecomprising a seal of a first outer film layer to a second outer filmlayer. The first outer film layer comprises a composition. Thecomposition comprises a first component and a second component. Thefirst component comprises at least one member selected from the groupconsisting of ethylene/vinyl acetate copolymer, and ethylene/acrylatecopolymer. The second component comprises at least one member selectedfrom the group consisting of elastomer, plastomer, and carboxyl-modifiedpolyethylene. The second outer film layer comprises at least one memberselected from the group consisting of ionomer, ethylene/acid copolymer,ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer.

Preferably, the ethylene/vinyl acetate copolymer has a vinyl acetate(polymerization unit) content of from about 1 to 26 weight percent; morepreferably, from about 4.5 to 19 weight percent; an still morepreferably, from about 6 to 19 weight percent.

Preferably, the ethylene/vinyl acetate copolymer has a density of fromabout 0.91 to 0.95 g/cc; more preferably, from about 0.92 to 0.95; stillmore preferably, from about 0.93 to 0.95. Preferably, theethylene/acrylate copolymer has a density of from about 0.91 to 0.95g/cc; more preferably, from about 0.92 to 0.95; still more preferably,from about 0.93 to 0.95.

As a third aspect, the present invention pertains to a packagecomprising a seal of a region of a first outer film layer to a region ofa second outer film layer. Each of the outer film layers comprises acomposition. The composition comprises a first component and a secondcomponent. The first component comprises at least one member selectedfrom the group consisting of polyethylene homopolymer,ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, andethylene/acrylate copolymer. The second component comprises at least onemember selected from the group consisting of elastomer, plastomer,ionomer, and carboxyl-modified polyethylene.

As a fourth aspect, the present invention pertains to a multilayer film.The multilayer film comprises an outer sealant layer and a coreseal-assist layer. The outer sealant layer comprises at least one memberselected from the group consisting of ionomer, carboxyl-modifiedpolyethylene, and ethylene/acid copolymer. The outer sealant layer has athickness of from about 1 percent to 20 percent, based on a totalthickness of the multilayer film; preferably 5 to 15 percent; morepreferably 7 to 10 percent; still more preferably 6 to 8 percent.Preferably, the seal-assist layer has a thickness of from about 10 to 95percent, based on the total thickness of the film; more preferably, fromabout 10 to 50 percent; still more preferably, from about 10 to 30percent. Preferably, the total thickness of the outer seal layertogether with the seal-assist layer is from about 0.15 to 3 mils; morepreferably, from about 0.5 to 2 mils; still more preferably, from about0.5 to 1 mil.

The core seal-assist layer comprises a composition. The compositioncomprises a first component and a second component. The first componentcomprises at least one member selected from the group consisting ofpolyethylene homopolymer, ethylene/alpha-olefin copolymer,ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer. Thesecond component comprises at least one member selected from the groupconsisting of elastomer, plastomer, ionomer, and carboxyl-modifiedpolyethylene.

As a fifth aspect, the present invention pertains to a packagecomprising a seal of a first region of a first outer film layer to asecond region of a second outer film layer. The first outer film layercomprises a homogeneous ethylene/alpha-olef in copolymer, and the secondouter film layer comprises at least one member selected from the groupconsisting of ionomer, ethylene/acid copolymer, carboxyl-modifiedpolyethylene. The seal has a strength of at least 2 lb/in; preferably astrength of from about 2 to 10 lb/in.; more preferably from about 3 to10 lb/in.; still more preferably, from about 5 to 10 lb/in.

As a sixth aspect, the present invention pertains to a film comprising acomposition. The composition comprises a first component and a secondcomponent. The first component comprises at least one member selectedfrom the group consisting of polyethylene homopolymer,ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, andethylene/acrylate copolymer. The second component comprises at least onemember selected from the group consisting of elastomer, plastomer, andcarboxyl-modified polyethylene.

As a seventh aspect, the present invention pertains to a film comprisinga first layer, a second layer, and a third layer. The first layer is anouter sealant layer, and the first layer comprises a first composition.The first composition comprises a first component and a secondcomponent. The first component comprises at least one member selectedfrom the group consisting of polyethylene homopolymer,ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, andethylene/acrylate copolymer. The second component comprises at least onemember selected from the group consisting of elastomer, plastomer, andcarboxyl-modified polyethylene. The second layer comprising a secondcomposition. The second composition comprises a third component and afourth component. The third component comprises at least one memberselected from the group consisting of polyethylene homopolymer,ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, andethylene/acrylate copolymer. The fourth component comprises at least onemember selected from the group consisting of elastomer, plastomer,ionomer, and carboxyl-modified polyethylene. The first composition isdifferent from the second composition.

As an eighth aspect, the present invention pertains to a multilayer filmcomprising a first layer and a second layer. The first layer is aseal-assist layer, and the first layer comprises a first composition.The first composition comprises a first component and a secondcomponent. The first component comprises at least one member selectedfrom the group consisting of polyethylene homopolymer,ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, andethylene/acrylate copolymer. The second component comprises at least onemember selected from the group consisting of elastomer, plastomer, andcarboxyl-modified polyethylene. The second layer is an outer sealantlayer, and the outer sealant layer comprising at least one memberselected from the group consisting of ionomer, ethylene/acid copolymer,and carboxyl modified polyethylene.

As a ninth aspect, the present invention pertains to a multilayer filmcomprising a first layer, a second layer, a third layer, a fourth layer,a fifth layer, and a sixth layer. The first layer is an outer sealantlayer as well as a food-contact layer, and the first layer comprises atleast one member selected from the group consisting of ionomer,ethylene/acid copolymer, and carboxyl-modified polyethylene. The secondlayer is an. outer layer as well as being a non-food-contact layer. Thethird layer is a seal-assist layer, and the third layer is between thefirst layer and the second layer. The third layer comprises a firstcomposition. The first composition comprises a first component and asecond component. The first component comprises at least one memberselected from the group consisting of polyethylene homopolymer,ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, andethylene/acrylate copolymer. The second component comprises at least onemember selected from the group consisting of elastomer, plastomer,ionomer, and carboxyl-modified polyethylene. The fourth layer is amemory layer, and the fourth layer is between the second layer and thethird layer. The fifth layer is a tie layer, and the fifth layer isbetween the third layer and the fourth layer. The sixth layer is a tielayer, and the sixth layer is between the second layer and the fourthlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an enlarged cross-sectional view of a monolayer filmin accord with the present invention.

FIG. 2 illustrates an enlarged cross-sectional view of a two-layer filmin accord with the present invention.

FIG. 3 illustrates an enlarged cross-sectional view of a three-layerfilm in accord with the present invention.

FIG. 4 illustrates an enlarged cross-sectional view of a four-layer filmin accord with the present invention.

FIG. 5 illustrates an enlarged cross-sectional view of a nine-layer filmin accord with the present invention.

FIG. 6 illustrates an enlarged cross-sectional view of an eight-layerfilm in accord with the present invention.

FIG. 7 illustrates an enlarged cross-sectional view of a seven-layerfilm in accord with the present invention.

FIG. 8 illustrates an enlarged cross-sectional view of an alternativeeight-layer film in accord with the present invention.

FIG. 9 illustrates an enlarged cross-sectional view of a six-layer filmin accord with the present invention.

FIG. 10 illustrates a perspective view of a packaged product accordingto the present invention.

FIG. 11 illustrates a perspective view of an alternative packagedproduct according to the present invention.

FIG. 13 illustrates a perspective view of another alternative packagedproduct according to the present invention.

FIG. 14 illustrates a cross-sectional view, through section 14-14, ofthe packaged product illustrated in FIG. 13.

FIG. 15 illustrates a cross-sectional view of a generic seal used in apackage.

FIG. 16 illustrates a cross-sectional view of a lap seal.

FIG. 17 illustrates a cross-sectional view of a package comprising a finseal.

FIG. 18 illustrates a schematic view of a preferred process for makingpreferred multilayer films.

FIG. 19 illustrates a schematic view of another preferred process formaking preferred multilayer films.

FIG. 20 illustrates a schematic view of another preferred process formaking preferred multilayer films.

FIG. 21 illustrates a schematic view of another preferred process formaking preferred multilayer films.

FIG. 22 is a bar graph representation of seal temperature (° F.) vs.seal strength (lb/in) results, and provides comparative data for theseal strengths of several sealants versus temperature.

FIG. 23 is a bar graph representation of seal temperature (° F.) vs.seal strength (lb/in) results, and provides comparative data for theseal strength of various ionomer resins as a function of temperature.

FIG. 24 is a bar graph representation of seal temperature (° F.) vs.seal strength (lb/in) results, and provides comparative data for theseal strength of various compositions in comparison with a specificionomer resin.

FIG. 25 is a bar graph representation of seal temperature (° F.) vs.seal strength (lb/in) results, and provides comparative data for theseal strength of various compositions being sealed to a specific ionomerresin.

FIG. 26 is a bar graph representation of seal temperature (° F.) vs.seal strength (lb/in) results, and provides comparative data for theseal strength of various compositions being sealed to a specific ionomerresin.

FIG. 27 is a bar graph representation of seal temperature (° F.) vs.seal strength (lb/in) results, and provides comparative data for theseal strength of an “ionomer capped” multilayer film to a specificionomer, versus a conventional ionomer to ionomer seal.

FIG. 28 is a bar graph representation of seal temperature (° F.) vs.seal strength (lb/in) results, and provides comparative data for theseal strength for two multilayer film structures versus a conventionalionomer to ionomer seal.

FIG. 29 is a bar graph representation of seal temperature (° F.) vs.seal strength (lb/in) results, and provides comparative data for theseal strength for a specific “ionomer capped” multilayer film to aspecific ionomer, versus a conventional ionomer to ionomer seal.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “film” is used in a generic sense to includeplastic web, regardless of whether it is film or sheet. Preferably,films of and used in the present invention have a thickness of 0.25 mmor less. As used herein, the term “package” refers to packagingmaterials used in the packaging of a product.

As used herein, the term “plastomer” refers to any of a family ofthermoplastic-elastomeric, styrene/butadiene copolymers whose moleculeshave a radial or star structure in which several polybutadiene chainsextend from a central hub, with a polystyrene block at the outward endof each segment. Preferably, the plastomer comprises homogeneousethylene/alpha olefin copolymer; more preferably, homogeneousethylene/alpha-olefin copolymer having a density of from about 0.86 to0.91; still more preferably, homogeneous ethylene/alpha-olefin copolymerhaving a density of from about 0.86 to 0.879. As used herein, the termplastomer is inclusive of such copolymers regardless of whether thecopolymer is cured or uncured.

As used herein, the term “elastomer” refers to a material that at roomtemperature can be stretched repeatedly to at least twice its originallength and, immediately upon release of the stress, returns with forceto its approximate original length. This characteristic distinguishesplastics from elastomers and rubbers, as well as the fact thatelastomers are given their final properties by mastication with fillers,processing aids, antioxidants, curing agents, etc., followed byvulcanization (curing) at elevated temperatures. Only a few elastomersare thermoplastic in nature. As used herein, the term “elastomer” isinclusive of: thermoplastic elastomers (“TPE'S”) such as ethylenepropylene diene monomer (“EPDM”), butyl rubber, styrene-butadiene blockcopolymer, chlorinated butyl rubber, and ethylene propylene rubber,thermoplastic urethane (“TPU”), thermoplastic olefin (“TPO”); andethylene propylene rubber (“EPR”). As used herein, the term elastomer isinclusive of such materials regardless of whether the material is curedor uncured.

Preferably, the elastomer used in the present invention comprises atleast one member selected from the group consisting of:acrylonitrile/chloroprene copolymer, acrylonitrile/isoprene copolymer,butadiene/acrylonitrile copolymer, chlorinated polyethylene,chlorosulfonated polyethylene, ethylene ether polysulfide,ethylene/ethyl acrylate copolymer, ethylene polysulfide,ethylene/propylene copolymer, ethylene/propylene/diene terpolymer,fluoroelastomer, fluorosilicone, hexafluoropropylene/vinylidene fluoridecopolymer, isobutene/isoprene copolymer, organopolysiloxane, acrylicester/butadiene copolymer, polybutadiene, polychloroprene,polyepichlorohydrin, polyisobutene, polyisoprene, polyurethane(polyester), polyurethane (polyether), polyurethane (polyether andpolyester), styrene/butadiene copolymer, styrene/chloroprene copolymer,polyethylene/butyl graft copolymer, and styrene/butadiene/styrenetriblock polymer.

The term “ionomer”, as used herein, refers to a product of an ionicpolymerization, i.e., a polymer containing interchain ionic bonding.Preferably, the ionomer comprises at least one member selected from thegroup consisting of a thermoplastic resin based on metal salt of analkene/acid copolymer; more preferably, a thermoplastic resin based onmetal salt of ethylene/acid copolymer; still more preferably,ethylene/methacrylic acid copolymer. As used herein, the term “ionomer”also includes ethylene/acrylic acid copolymer and ethylene/acid/acrylateterpolymer.

As used herein, the phrase “carboxyl-modified polyethylene” refers to aclass of polymers which are similar to ionomers, but which are hereinconsidered to be chemically distinct from ionomers. Carboxyl-modifiedpolyethylene, also referred to as “EMA ionomer”, is produced frommetal-based materials such as zinc acetate or sodium hydroxide reactedwith ethylene/methacrylate copolymer, as is known to those of skill inthe polymer art. Ethylene/butyl acrylate copolymer is anothercarboxyl-modified polyethylene.

As used herein, the phrases “seal layer”, “sealing layer”, “heat seallayer”, and “sealant layer”, refer to an outer film layer, or layers,involved in the sealing of the film to itself, another film layer of thesame or another film, and/or another article which is not a film. Itshould also be recognized that in general, up to the outer 3 mils of afilm can be involved in the sealing of the film to itself or anotherlayer. With respect to packages having only fin-type seals, as opposedto lap-type seals, the phrase “sealant layer” generally refers to theinside film layer of a package, as well as supporting layers adjacentthis sealant layer often being sealed to itself, and frequently servingas a food contact layer in the packaging of foods. In general, a sealantlayer sealed by heat-sealing layer comprises any thermoplastic polymer;preferably, the heat-sealing layer comprises, for example, thermoplasticpolyolefin, thermoplastic polyamide, thermoplastic polyester, andthermoplastic polyvinyl chloride; more preferably, thermoplasticpolyolefin; still more preferably, thermoplastic polyolefin having lessthan 60 weight percent crystallinity.

As used herein, the term “seal” refers to any seal of a first region ofa film surface to a second region of a film surface, wherein the seal isformed by heating the regions to at least their respective sealinitiation temperatures. The heating can be performed by any one or moreof a wide variety of manners, such as using a heated bar, hot air,infrared radiation, ultrasonic sealing, etc.

As used herein, the phrase “non-contact sealant layer” refers to anouter film layer which is suitable for use as a sealant layer, butwhich, when the film is used to make a package, is the film layer on theoutside of the package, and therefore has no substantial direct contactwith the product within the package. The non-contact sealant layer cancomprise a composition comprising a homogeneous ethylene/alpha-olefincopolymer and a homogeneous ethylene/alpha-olefin copolymer plastomer;preferably, the non-contact sealant layer comprises anethylene/alpha-olefin copolymer; more preferably, the non-contactsealant layer comprises a homogeneous ethylene/alpha-olefin copolymer.

As used herein, the phrase “seal-assist layer” refers to a core layer ofa multilayer film which is within about 3 mils of an outer surface ofthe film, this core layer having a seal initiation temperature no higherthan the temperature this layer reaches during a heat sealing operation.

As used herein, with respect to the seal layer and/or the seal-assistlayer, if the “composition” present in one or more of these layerscomprises a “first component” and a “second component”, or if thecomposition comprises a “third component” and a “fourth component”, thetwo components in the layer are polymeric components which aresubstantially uniformly intermixed, i.e., uniformly blended, with oneanother, so that the composition is substantially homogeneous withrespect to the presence of both the first component and the secondcomponent.

Furthermore, the components in the composition used in the presentinvention are different components. For example, if the first componentis an ethylene/alpha-olefin copolymer, and the second component is ahomogeneous ethylene/alpha-olefin copolymer plastomer, although thefirst component can also be a homogeneous ethylene/alpha-olefincopolymer plastomer, the first component must be chemically differentfrom the second component. As a first preferred difference, the firstcomponent has a density of from about 0.88 to 0.92 g/cc (morepreferably, 0.89 to 0.92; still more preferably, 0.90 to 0.92, and yetstill more preferably, 0.90 to 0.915), whereas the second component hasa density of from about 0.86 to 0.91 g/cc (more preferably, 0.86 to0.879).

As an alternative difference between the first component and the secondcomponent in the composition, there is a difference in the VicatSoftening Point between the two components. Vicat Softening Point is thetemperature at which a flat-nosed needle of 1 mm² circular cross sectionpenetrates a thermoplastic specimen to a depth of 1 mm under a specifiedload using a uniform rate of temperature rise (ASTM D 1525, herebyincorporated by reference thereto, in its entirety). Preferably thefirst component has a Vicat Softening Point of from 10° C. to 100° C.higher than the Vicat Softening Point of the second component; morepreferably 10° C. to 75° C. higher; still more preferably, 20° C. to 50°C. higher. However, the greater the difference in Vicat Softening Point,the greater the potential for enhancing the advantages provided by thepresent invention.

The outer sealant layer, in film according to the present invention, canfurther comprise an anhydride functionality. The presence of theanhydride functionality is especially advantageous if the film is to beused in a cook-in application, and the outer sealant layer is to be indirect contact with a product comprising meat. The anhydridefunctionality increases the degree of meat adhesion obtained, therebypreventing purge during cook-in. This subject matter is discussed indetail in copending U.S. patent application Ser. No. ______, filed Apr.18, 1994, entitled “Film Having Anhydride Functionality in Outer Layer,Process for Making Same, Packaging Using Same, and Packaged ProductComprising Same”, which is hereby incorporated by reference thereto, inits entirety.

As used herein, the term “barrier”, and the phrase “barrier layer”, asapplied to films and/or film layers, is used with reference to theability of a film or film layer to serve as a barrier to one or moregases. Oxygen (i.e., O₂) barrier layers can comprise, for example,ethylene/vinyl alcohol copolymer, polyvinyl chloride, polyvinylidenechloride, polyamide, polyester, polyacrylonitrile, etc., as known tothose of skill in the art; preferably, the oxygen barrier layercomprises ethylene/vinyl alcohol copolymer, polyvinyl chloride,polyvinylidene chloride, and polyamide; more preferably, ethylene/vinylalcohol copolymer.

As used herein, the phrase “abuse layer” refers to an outer film layerand/or an inner film layer, so long as the film layer serves to resistabrasion, puncture, and other potential causes of reduction of packageintegrity, as well as potential causes of reduction of packageappearance quality. Abuse layers can comprise any polymer, so long asthe polymer contributes to achieving an integrity goal and/or anappearance goal; preferably, abuse layers comprise polymer having amodulus of at least 10⁷ Pascals, at room temperature; more preferably,the abuse layer comprises at least one member selected from the groupconsisting of polyamide, ethylene/propylene copolymer; more preferably,nylon 6, nylon 6/6, amorphous nylon, and ethylene/propylene copolymer.

As used herein, the term “core”, and the phrase “core layer”, as appliedto multilayer films, refer to any internal film layer which has aprimary function other than serving as an adhesive or compatibilizer foradhering two layers to one another. Usually, the core layer or layersprovide the multilayer film with a desired level of strength, i.e.,modulus, and/or optics, and/or added abuse resistance, and/or specificimpermeability.

As used herein, the phrase “skin layer” refers to an outside layer of amultilayer film in packaging a product, this skin layer being subject toabuse. Accordingly, the preferred polymers for the skin layer are thesame as the preferred polymers for the abuse layer.

As used herein, the phrase “tie layer” refers to any internal layerhaving the primary purpose of adhering two layers to one another. Tielayers can comprise any nonpolymer polymer having a polar group graftedthereon, so that the polymer is capable of covalent bonding to polarpolymers such as polyamide and ethylene/vinyl alcohol copolymer;preferably, tie layers comprise at least one member selected from thegroup consisting of modified polyolefin, modified ethylene/vinyl acetatecopolymer, and homogeneous ethylene/alpha-olefin copolymer; morepreferably, tie layers comprise at least one member selected from thegroup consisting of anhydride modified grafted linear low densitypolyethylene, anhydride grafted low density polyethylene, homogeneousethylene/alpha-olefin copolymer, and anhydride grafted ethylene/vinylacetate copolymer.

As used herein, the phrase “bulk layer” refers to any layer of a filmwhich is present for the purpose of increasing the abuse-resistance,toughness, modulus, etc., of a multilayer film. Bulk layers generallycomprise polymers which are inexpensive relative to other polymers inthe film which provide some specific purpose unrelated toabuse-resistance, modulus, etc. Preferably, bulk layers comprisepolyolefin; more preferably, at least one member selected from the groupconsisting of ethylene/alpha-olefin copolymer, ethylene/alpha-olefincopolymer plastomer, low density polyethylene, and linear low densitypolyethylene.

The names “first layer”, “second layer”, as used herein, are generallyindicative of the manner in which a multilayer film structure is builtup. That is, in general, the first layer can be present without any ofthe additional layers described, or the first and second layers can bepresent without any of the additional layers described, etc.

As used herein, the phrase “thermoforming layer” refers to a film layerwhich can be heated and drawn into a cavity while maintaining uniformthinning, as opposed films or film layers which lose integrity duringthe thermoforming process (e.g. polyethylene homopolymers do not undergothermoforming with uniform thinning). Preferably, thermoforming layerscomprise polyamide, ethylene/propylene copolymer, and propylenehomopolymer; more preferably, nylon 6, nylon 6/6, amorphous nylon,ethylene/propylene copolymer, and propylene homopolymer.

As used herein, the phrase “heat-resistant layer” refers to a film layerwhich has a relatively high melt temperature and/or relatively high heatdistortion temperature, relative to the remainder of the film,especially relative to the sealant layer(s). Preferably, heat-resistantlayers comprise at least one member selected from the group consistingof polyamide and propylene homopolymer; more preferably, nylon 6, nylon6/6, amorphous nylon, and propylene homopolymer.

As used herein, the phrase “ultraviolet-protection layer” refers to afilm layer which have the capability of absorbing ultraviolet radiation,so that the ultraviolet radiation cannot penetrate the film and beabsorbed by-the product. Preferably, ultraviolet-protection layerscomprise a polyamide; more preferably, at least one member selected fromthe group consisting nylon 6 and amorphous nylon.

As used herein, the phrase “memory layer” refers to a film layer whichhas elastic characteristics below its plastic deformation point, i.e.,elongation at yield. Memory layers can comprise any polymer which hasrelatively high elongation at yield; preferably, memory layers comprisea polyamide; more preferably, nylon 6.

As used herein, the phrase “meat-contact layer”, refers to a layer of amultilayer film which is in direct contact with the meat-containingproduct packaged in the film. The meat-contact layer is an outer layer,in order to be in direct contact with the meat product. The meat-contactlayer is an inside layer in the sense that in the packaged meat product,the meat-contact layer is the innermost film layer in direct contactwith the food.

As used herein, the phrase “meat-contact surface” refers to a surface ofa meat-contact layer which is in direct contact with the meat in thepackage.

As used herein, the phrase “cook-in” refers to the process of cooking aproduct packaged in a material capable of withstanding exposure to longand slow cooking conditions while containing the food product, forexample submersion in water at 57° C. to 121° C. (i.e, 135° F.-250° F.)for 2-12 hours, preferably 57° C. to 100° C. (i.e, 135° F.-250° F.) for2-12 hours. Cook-in packaged foods are essentially pre-packaged,pre-cooked foods which may be directly transferred to the consumer inthis form. These types of foods may be consumed with or without warming.Cook-in packaging materials maintain seal integrity, and in the case ofmultilayer films are delamination resistant. Cook-in films must also beheat shrinkable under cook-in conditions so as to form a tightly fittingpackage. Cook-in films preferably have a tendency for adhesion to thefood product, thereby preventing “cook-out”, which is the collection ofjuices between the outer surface of the food product and themeat-contact surface of the film, i.e., the surface in direct contactwith the meat. Additional optional characteristics of films for use incook-in applications include delamination-resistance, low 02permeability, heat-shrinkability representing about 20-50% biaxialshrinkage at about 85° C. (185° F.), and optical clarity.

As used herein, “EVOH” refers to ethylene vinyl alcohol copolymer. EVOHincludes saponified or hydrolyzed ethylene vinyl acetate copolymers, andrefers to a vinyl alcohol copolymer having an ethylene comonomer, andprepared by, for example, hydrolysis of vinyl acetate copolymers, or bychemical reactions with polyvinyl alcohol. The degree of hydrolysis ispreferably at least 50% and more preferably at least 85%.

As used herein, the term “lamination”, the term “laminate”, and thephrase “laminated film”, refer to the process, and resulting product,made by bonding together two or more layers of film or other materials.Lamination can be accomplished by joining layers with adhesives, joiningwith heat and pressure, and even spread coating and extrusion coating.The term laminate is also inclusive of coextruded multilayer filmscomprising one or more tie layers.

As used herein, the term “oriented” refers to a polymer-containingmaterial which has been stretched at an elevated temperature (theorientation temperature), followed by being “set” in the stretchedconfiguration by cooling the material while substantially retaining thestretched dimensions. Upon subsequently heating unrestrained,unannealed, oriented polymer-containing material to its orientationtemperature, heat shrinkage is produced almost to the originalunstretched, i.e., pre-oriented dimensions. More particularly, the term“oriented”, as used herein, refers to oriented films, wherein theorientation can be produced in one or more of a variety of manners.

As used herein, the phrase “orientation ratio” refers to themultiplication product of the extent to which the plastic film materialis expanded in several directions, usually two directions perpendicularto one another. Expansion in the machine direction is herein referred toas “drawing”, whereas expansion in the transverse direction is hereinreferred to as “stretching”. The degree of orientation is also referredto as the orientation ratio, or sometimes as the “racking ratio”.

As used herein, the term “monomer” refers to a relatively simplecompound, usually containing carbon and of low molecular weight, whichcan react to form a polymer by combining with itself or with othersimilar molecules or compounds.

As used herein, the term “comonomer” refers to a monomer which iscopolymerized with at least one different monomer in a copolymerizationreaction, the result of which is a copolymer.

As used herein, the term “polymer” refers to the product of apolymerization reaction, and is inclusive of homopolymers, copolymers,terpolymers, etc. In general, the layers of a film can consistessentially of a single polymer, or can have still additional polymerstogether therewith, i.e., blended therewith.

As used herein, the term “homopolymer” is used with reference to apolymer resulting from the polymerization of a single monomer, i.e., apolymer consisting essentially of a single type of repeating unit.

As used herein, the term “copolymer” refers to polymers formed by thepolymerization reaction of at least two different monomers. For example,the term “copolymer” includes the copolymerization reaction product ofethylene and an alpha-olefin, such as 1-hexene. However, the term“copolymer” is also inclusive of, for example, the copolymerization of amixture of ethylene, propylene, 1-hexene, and 1-octene.

As used herein, the term “polymerization” is inclusive ofhomopolymerizations, copolymerizations, terpolymerizations, etc., andincludes all types of copolymerizations such as random, graft, block,etc. In general, the polymers, in the films used in accordance with thepresent invention, can be prepared in accordance with any suitablepolymerization process, including slurry polymerization, gas phasepolymerization, and high pressure polymerization processes.

Slurry polymerization processes generally use superatmospheric pressuresand temperatures in the range of 40°-100° C. In a slurry polymerization,a suspension of solid, particulate polymer is formed in a liquidpolymerization medium to which ethylene and comonomers and oftenhydrogen along with catalyst are added. The liquid employed in thepolymerization medium can be an alkane, cycloalkane, or an aromatichydrocarbon such as toluene, ethylbenzene or xylene. The medium employedshould be liquid under the conditions of polymerization, and relativelyinert. Preferably, hexane or toluene is employed.

Alternatively, gas-phase polymerization process utilizessuperatmospheric pressure and temperature in the range of about 50°-120°C. Gas phase polymerization can be performed in a stirred or fluidizedbed of catalyst and product particles in a pressure vessel adapted topermit the separation of product particles from unreacted gases.Ethylene, comonomer, hydrogen and an inert diluent gas such as nitrogencan be introduced or recirculated so as to maintain the particles attemperatures of 50°-120° C. Triethylaluminum may be added as needed as ascavenger of water, oxygen, and other impurities. Polymer product can bewithdrawn continuously or semicontinuously, at a rate such as tomaintain a constant product inventory in the reactor. Afterpolymerization and deactivation of the catalyst, the product polymer canbe recovered by any suitable means. In commercial practice, the polymerproduct can be recovered directly from the gas phase reactor, freed ofresidual monomer with a nitrogen purge, and used without furtherdeactivation or catalyst removal.

High pressure polymerization processes utilize a catalyst systemcomprising a cyclopentadienyl-transition metal compound and an alumoxanecompound. It is important, in the high-pressure process, that thepolymerization temperature be above about 120° C., but below thedecomposition temperature of the polymer product. It is also importantthat the polymerization pressure be above about 500 bar (kg/cm²). Inthose situations wherein the molecular weight of the polymer productthat would be produced at a given set of operating conditions is higherthan desired, any of the techniques known in the art for control ofmolecular weight, such as the use of hydrogen or reactor temperature,may be used in the process of this invention.

As used herein, the term “copolymerization” refers to the simultaneouspolymerization of two or more monomers.

As used herein, a copolymer identified in terms of a plurality ofmonomers, e.g., “propylene/ethylene copolymer”, refers to a copolymer inwhich either monomer copolymerizes in a higher weight or molar percent.However, the first listed monomer preferably is polymerizes in a higherweight percent than the second listed monomer, and, for copolymers whichare terpolymers, quadripolymers, etc., preferably, the first monomercopolymerizes in a higher weight percent than the second monomer, andthe second monomer copolymerizes in a higher weight percent than thethird monomer, etc.

As used herein, copolymers are identified, i.e, named, in terms of themonomers from which the copolymers are produced. For example, the phrase“propylene/ethylene copolymer” refers to a copolymer produced by thecopolymerization of both propylene and ethylene, with or withoutadditional comonomer(s). A copolymer comprises recurring “polymerizationunits” derived from the monomers from which the copolymer is produced.

As used herein, the phrase “polymerization unit” refers to a unit of apolymer, as derived from a monomer used in the polymerization reaction.For example, the phrase “alpha-olefin polymerization units” refers to aunit in, for example, an ethylene/alpha-olefin copolymer, thepolymerization unit being that residue which is derived from thealpha-olefin monomer after it reacts to become a portion of the polymerchain.

Either of the named monomers may copolymerize in a higher weight ormolar percent. However, the first listed monomer preferably polymerizesin a higher weight percent than the second listed monomer, and, forcopolymers which are terpolymers, quadripolymers, etc., preferably themonomer specified first in the name, i.e, the first-specified monomer,copolymerized in a higher weight percent than the second-specifiedmonomer, and in turn the second-specified monomer copolymerizes in ahigher weight percent than the third-specified monomer, etc.

As used herein, terminology employing a “/” with respect to the chemicalidentity of a copolymer (e.g., “an ethylene/alpha-olefin copolymer”),identifies the comonomers which are copolymerized to produce thecopolymer. Such phrases as “ethylene alpha-olefin copolymer” is therespective equivalent of “ethylene/alpha-olefin copolymer.”

As used herein, the phrase “heterogeneous polymer” refers topolymerization reaction products of relatively wide variation inmolecular weight and relatively wide variation in compositiondistribution, i.e., polymers made, for example, using conventionalZiegler-Natta catalysts. Heterogeneous polymers are useful in variouslayers of the film used in the present invention. Such polymerstypically contain a relatively wide variety of chain lengths andcomonomer percentages.

As used herein, the phrase “heterogeneous catalyst” refers to a catalystsuitable for use in the polymerization of heterogeneous polymers, asdefined above. Heterogeneous catalysts are comprised of several kinds ofactive sites which differ in Lewis acidity and steric environment.Ziegler-Natta catalysts are heterogeneous catalysts. Examples ofZiegler-Natta heterogeneous systems include metal halides activated byan organometallic co-catalyst, such as titanium chloride, optionallycontaining magnesium chloride, complexed to trialkyl aluminum and may befound in patents such as U.S. Pat. No. 4,302,565, to GOEKE, et. al., andU.S. Pat. No. 4,302,566, to KAROL, et. al., both of which are herebyincorporated, in their entireties, by reference thereto.

As used herein, the phrase “homogeneous polymer” refers topolymerization reaction products of relatively narrow molecular weightdistribution and relatively narrow composition distribution. Homogeneouspolymers are useful in various layers of the multilayer film used in thepresent invention. Homogeneous polymers exhibit a relatively evensequencing of comonomers within a chain, the mirroring of sequencedistribution in all chains, and the similarity of length of all chains,and are typically prepared using metallocene, or other single-site typecatalysis.

More particularly, homogeneous ethylene/alpha-olefin copolymers may becharacterized by one or more methods known to those of skill in the art,such as molecular weight distribution (M_(W)/M_(n)), compositiondistribution breadth index (CDBI), and narrow melting point range andsingle melt point behavior. The molecular weight distribution(M_(W/)M_(n)), also known as polydispersity, may be determined by gelpermeation chromatography. The homogeneous ethylene/alpha-olefincopolymers useful in this invention will have a (M_(W)/M_(n)) of lessthan 2.7. Preferably, the (M_(W)/M_(n)) will have a range of about 1.9to 2.5. More preferably, the (M_(W)/M_(n)) will have a range of about1.9 to 2.3. The composition distribution breadth index (CDBI) of suchhomogeneous ethylene/alpha-olefin copolymers will generally be greaterthan about 70 percent. The CDBI is defined as the weight percent of thecopolymer molecules having a comonomer content within 50 percent (i.e.,plus or minus 50%) of the median total molar comonomer content. The CDBIof linear polyethylene, which does not contain a comonomer, is definedto be 100%. The Composition Distribution Breadth Index (CDBI) isdetermined via the technique of Temperature Rising Elution Fractionation(TREF). CDBI determination clearly distinguishes the homogeneouscopolymers used in the present invention (narrow compositiondistribution as assessed by CDBI values generally above 70%) from VLDPEsavailable commercially which generally have a broad compositiondistribution as assessed by CDBI values generally less than 55%. TheCDBI of a copolymer is readily calculated from data obtained fromtechniques known in the art, such as, for example, temperature risingelution fractionation as described, for example, in Wild et. al., J.Poly. Sci. Poly. Phys. Ed., Vol. 20, p.441 (1982). Preferably, thehomogeneous ethylene/alpha-olefin copolymers have a CDBI greater thanabout 70%, i.e., a CDBI of from about 70% to 99%. In general, thehomogeneous ethylene/alpha-olefin copolymers in the multilayer films ofthe present invention also exhibit a relatively narrow melting pointrange, in comparison with “heterogeneous copolymers”, i.e., polymershaving a CDBI of less than 55%. Preferably, the homogeneousethylene/alpha-olefin copolymers exhibit an essentially singular meltingpoint characteristic, with a peak melting point (T_(m)), as determinedby Differential Scanning Colorimetry (DSC), of from about 60° C. to 110°C. Preferably the homogeneous copolymer has a DSC peak T_(m) of fromabout 80° C. to 100° C. As used herein, the phrase “essentially singlemelting point” means that at least about 80%, by weight, of the materialcorresponds to a single T_(m) peak at a temperature within the range offrom about 60° C. to 110° C., and essentially no substantial fraction ofthe material has a peak melting point in excess of about 115° C., asdetermined by DSC analysis. DSC measurements are made on a Perkin ElmerSystem 7 Thermal Analysis System. Melting information reported aresecond melting data, i.e., the sample is heated at a programmed rate of10° C./min. to a temperature below its critical range. The sample isthen reheated (2nd melting) at a programmed rate of 10° C./min. Thepresence of higher melting peaks is detrimental to film properties suchas haze, and compromises the chances for meaningful reduction in theseal initiation temperature of the final film.

A homogeneous ethylene/alpha-olefin copolymer can, in general, beprepared by the copolymerization of ethylene and any one or morealpha-olefin. Preferably, the alpha-olefin is a C₃-C₂₀ alpha-monoolefin,more preferably, a C₄-C₁₂ alpha-monoolefin, still more preferably, aC₄-C₈ alpha-monoolefin. Still more preferably, the alpha-olefincomprises at least one member selected from the group consisting ofbutene-1, hexene-1, and octene-1, i.e., 1-butene, 1-hexene, and1-octene, respectively. Most preferably, the alpha-olefin comprisesoctene-1, and/or a blend of hexene-1 and butene-1.

Processes for preparing homogeneous polymers are disclosed in U.S. Pat.Nos. 5,206,075, 5,241,031, and PCT International Application WO93/03093, each of which is hereby incorporated by reference thereto, inits entirety. Further details regarding the production and use of onegenus of homogeneous ethylene/alpha-olefin copolymers are disclosed inU.S. Pat. No. 5,206,075, to HODGSON, Jr.; U.S. Pat. No. 5,241,031, toMEHTA; PCT International Publication Number WO 93/03093, in the name ofExxon Chemical Company; PCT International Publication Number WO90/03414, in the name of Exxon Chemical Patents, Inc., all four of whichare hereby incorporated in their entireties, by reference there. Stillanother genus of homogeneous ethylene/alpha-olefin copolymers isdisclosed in U.S. Pat. No. 5,272,236, to LAI, et. al., and U.S. Pat. No.5,278,272, to LAI, et. al., both of which are hereby incorporated intheir entireties, by reference thereto.

As used herein, the phrase “homogeneous catalyst” refers to a catalystsuitable for use in the polymerization of homogeneous polymers, asdefined above. Homogeneous catalysts are also referred to as “singlesite catalysts”, due to the fact that such catalysts typically have onlyone type of catalytic site, which is believed to be the basis for thehomogeneity of the polymers they catalyze the polymerization of.

As used herein, the term “polyolefin” refers to any polymerized olefin,which can be linear, branched, cyclic, aliphatic, aromatic, substituted,or unsubstituted. More specifically, included in the term polyolefin arehomopolymers of olefin, copolymers of olefin, copolymers of an olefinand an non-olefinic comonomer copolymerizable with the olefin, such asvinyl monomers, modified polymers thereof, and the like. Specificexamples include polypropylene homopolymers, polyethylene homopolymers,poly-butene, propylene/alpha-olefin copolymers, ethylene/alpha-olefincopolymers, butene/alpha-olefin copolymers, ethylene/vinyl acetatecopolymers, ethylene/ethyl acrylate copolymers, ethylene/butyl acrylatecopolymers, ethylene/methyl acrylate copolymers, ethylene/acrylic acidcopolymers, ethylene/methacrylic acid copolymers, modified polyolefinresins, ionomer resins, polymethylpentene, etc. The modified polyolefinresins include modified polymers prepared by copolymerizing thehomopolymer of the olefin or copolymer thereof with an unsaturatedcarboxylic acid, e.g., maleic acid, fumaric acid or the like, or aderivative thereof such as the anhydride, ester or metal salt or thelike. It could also be obtained by incorporating into the olefinhomopolymer or copolymer, an unsaturated carboxylic acid, e.g., maleicacid, fumaric acid or the like, or a derivative thereof such as theanhydride, ester or metal salt or the like.

As used herein, terms identifying polymers, such as “polyamide”,“polyester”, “polyurethane”, etc. are inclusive of not only polymerscomprising repeating units derived from monomers known to polymerize toform a polymer of the named type, but are also inclusive of comonomers,derivatives, etc. which can copolymerize with monomers known topolymerize to produce the named polymer. For example, the term“polyamide” encompasses both polymers comprising repeating units derivedfrom monomers, such as caprolactam, which polymerize to form apolyamide, as well as copolymers derived from the copolymerization ofcaprolactam with a comonomer which when polymerized alone does notresult in the formation of a polyamide. Furthermore, terms identifyingpolymers are also inclusive of mixtures, blends, etc. of such polymerswith other polymers of a different type.

As used herein, the phrase “anhydride functionality” refers to any formof anhydride functionality, such as the anhydride of maleic acid,fumaric acid, etc., whether blended with one or more polymers, graftedonto a polymer, or copolymerized with a polymer, and, in general, isalso inclusive of derivatives of such functionalities, such as acids,esters, and metal salts derived therefrom.

As used herein, the phrase “modified polymer”, as well as more specificphrases such as “modified ethylene vinyl acetate copolymer”, and“modified polyolefin” refer to such polymers having ,an anhydridefunctionality, as defined immediately above, grafted thereon and/orcopolymerized therewith and/or blended therewith. Preferably, suchmodified polymers have the anhydride functionality grafted on orpolymerized therewith, as opposed to merely blended therewith.

As used herein, the phrase “anhydride-containing polymer” and“anhydride-modified polymer”, refers to one or more of the following:(1) polymers obtained by copolymerizing an anhydride-containing monomerwith a second, different monomer, and (2) anhydride grafted copolymers,and (3) a mixture of a polymer and an anhydride-containing compound.

As used herein, the phrase “ethylene alpha-olefin copolymer”, and“ethylene/alpha-olefin copolymer”, refer to such heterogeneous materialsas linear low density polyethylene (LLDPE), and very low and ultra lowdensity polyethylene (VLDPE and ULDPE); and homogeneous polymers such asmetallocene catalyzed polymers such as EXACT™ materials supplied byExxon, and TAFMER™ materials supplied by Mitsui PetrochemicalCorporation. These materials generally include copolymers of ethylenewith one or more comonomers selected from C₄ to C₁₀ alpha-olefin such asbutene-1 (i.e., 1-butene), hexene-1, octene-1, etc. in which themolecules of the copolymers comprise long chains with relatively fewside chain branches or cross-linked structures. This molecular structureis to be contrasted with conventional low or medium densitypolyethylenes which are more highly branched than their respectivecounterparts. LLDPE, as used herein, has a density usually in the rangeof from about 0.91 grams per cubic centimeter to about 0.94 grams percubic centimeter. Other ethylene/alpha-olefin copolymers, such as thelong chain branched homogeneous ethylene/alpha-olefin copolymersavailable from the Dow Chemical Company, known as AFFINITY™ resins, arealso included as another type of ethylene alpha-olefin copolymer usefulin the present invention.

In general, the ethylene/alpha-olefin copolymer comprises a copolymerresulting from the copolymerization of from about 80 to 99 weightpercent ethylene and from 1 to 20 weight percent alpha-olefin.Preferably, the ethylene alpha-olefin copolymer comprises a copolymerresulting from the copolymerization of from about 85 to 95 weightpercent ethylene and from 5 to 15 weight percent alpha-olefin.

As used herein, the phrases “inner layer” and “internal layer” refer toany layer, of a multilayer film, having both of its principal surfacesdirectly adhered to another layer of the film.

As used herein, the phrase “outer layer” refers to any film layer offilm having less than two of its principal surfaces directly adhered toanother layer of the film. The phrase is inclusive of monolayer andmultilayer films. In multilayer films, there are two outer layers, eachof which has a principal surface adhered to only one other layer of themultilayer film. In monolayer films, there is only one layer, which, ofcourse, is an outer layer in that neither of its two principal surfacesare adhered to another layer of the film.

As used herein, the phrase “inside layer” refers to the outer layer, ofa multilayer film packaging a product, which is closest to the product,relative to the other layers of the multilayer film.

As used herein, the phrase “outside layer” refers to the outer layer, ofa multilayer film packaging a product, which is furthest from theproduct relative to the other layers of the multilayer film.

As used herein, the phrase “directly adhered”, as applied to filmlayers, is defined as adhesion of the subject film layer to the objectfilm layer, without a tie layer, adhesive, or other layer therebetween.In contrast, as used herein, the word “between”, as applied to a filmlayer expressed as being between two other specified layers, includesboth direct adherence of the subject layer between to the two otherlayers it is between, as well as including a lack of direct adherence toeither or both of the two other layers the subject layer is between,i.e., one or more additional layers can be imposed between the subjectlayer and one or more of the layers the subject layer is between.

As used herein, the term “extrusion” is used with reference to theprocess of forming continuous shapes by forcing a molten plasticmaterial through a die, followed by cooling or chemical hardening.Immediately prior to extrusion through the die, the relativelyhigh-viscosity polymeric material is fed into a rotating screw ofvariable pitch, which forces it through the die.

As used herein, the term “coextrusion” refers to the process ofextruding two or more materials through a single die with two or moreorifices arranged so that the extrudates merge and weld together into alaminar structure before chilling, i.e., quenching. Coextrusion can beemployed in film blowing, free film extrusion, and extrusion coatingprocesses.

As used herein, the phrase “machine direction”, herein abbreviated “MD”,refers to a direction “along the length” of the film, i.e., in thedirection of the film as the film is formed during extrusion and/orcoating.

As used herein, the phrase “transverse direction”, herein abbreviated“TD”, refers to a direction across the film, perpendicular to themachine or longitudinal direction.

As used herein, the phrase “free shrink” refers to the percentdimensional change in a 10 cm×10 cm specimen of film, when subjected toselected heat, as measured by ASTM D 2732, as known to those of skill inthe art.

Although the majority of the above definitions are substantially asunderstood by those of skill in the art, one or more of the abovedefinitions may be defined hereinabove in a manner differing from themeaning as ordinarily understood by those of skill in the art, due tothe particular description herein of the present invention.

Discussion of the Figures

In general, the film used in the present invention can be a monolayerfilm or a multilayer film. The multilayer film illustrated in FIG. 1 isa monolayer film; in FIG. 2, two layers; in FIG. 3, three layers; inFIG. 4, four layers; in FIG. 5, nine layers; and in FIG. 6, eightlayers; in FIG. 7, seven layers; in FIG. 8, eight layers; in FIG. 9, sixlayers. Preferably, the film used in the present invention comprisesfrom 2 to 20 layers; more preferably, from 2 to 12 layers; and stillmore preferably, from 4 to 9 layers.

In general, the multilayer film used in the present invention can haveany total thickness desired, so long as the film provides the desiredproperties for the particular packaging operation in which the film isused. Preferably, the film used in the present invention has a totalthickness (i.e., a combined thickness of all layers), of from about 0.5to 15 mils (1 mil equals 0.001 inch); more preferably, from about 1 to10 mils; and still more preferably, from 2 to 8 mils.

In FIG. 1, monolayer film 30 is composed of a substantially homogeneouscomposition comprising a homogeneous ethylene/alpha-olefin copolymer, ahomogeneous ethylene/alpha-olefin copolymer plastomer, and low densitypolyethylene. Table I provides the structural and compositionalcharacteristics of this film. TABLE I percent of film total film typelayer function chemical identity thickness monolayer sealant, 60% 0.900g/cc homo- 100 bulk, etc. geneous Et/alpha-olefin; 35% 0.87 g/cc homo-geneous plastomer;  5% 0.923 g/cc LDPE

In FIG. 2, multilayer film 32 comprises outer sealant layer 34 andseal-assist layer 36. Preferably, sealant layer 34 is composed of anionomer resin, or a substantially homogeneous composition comprising ahomogeneous ethylene/alpha-olefin copolymer and a homogeneousethylene/alpha-olefin copolymer plastomer; preferably, seal-assist layer36 is composed of a substantially homogeneous composition comprising ahomogeneous ethylene/alpha-olefin copolymer and a homogeneousethylene/alpha-olefin copolymer plastomer. Tables II-A and II-B providetwo embodiments for the structural and compositional characteristics ofmultilayer film 32. TABLE II-A percent of layer total film designationlayer function chemical identity thickness 1 outer sealant ionomer 10 2seal-assist 65% 0.915 g/cc homo- 90 geneous ethylene/alpha- olefincopolymer; 35% 0.87 g/cc homogeneous ethylene/alpha-olefin copolymerplastomer

TABLE II-B provides an alternative to the multilayer film described inTABLE II-A. TABLE II-B percent of layer layer total film order namelayer function chemical identity thickness 1 second outer sealant 65%0.900 g/cc homo- 10 geneous ethylene/alpha- ; olefin copolymer; 35% 0.87g/cc homo- geneous ethylene/alpha- olefin copolymer plastomer 2 firstseal-assist 0.905 g/cc homogeneous 90 ethylene/alpha-olefin copolymer

In FIG. 3, multilayer film 38 comprises outer sealant layer 40,seal-assist layer 42, and bulk layer 44. Preferably, film 38 has a totalthickness of from about 0.5 to 8 mils; more preferably, 0.75 to 6 mils,and still more preferably from about 1.5 to 5 mils. Preferably, outersealant layer 40 is composed of an ionomer resin; preferably,seal-assist layer 42 is composed of a substantially homogeneouscomposition comprising a homogeneous ethylene/alpha-olefin copolymer anda homogeneous ethylene/alpha-olefin copolymer plastomer; and preferably,bulk layer 44 is composed of a substantially homogeneous blend of linearlow density polyethylene and low density polyethylene. Tables III-A andIII-B provide the structural and compositional characteristics ofpreferred embodiments of multilayer film 38. TABLE III-A percent oflayer layer total film order name layer function chemical identitythickness 1 second seal ionomer 7 2 first seal-assist 70% 0.900 g/cchomo- 20 geneous Et/alpha-olefin; 30% 0.88 g/cc homo- geneous plastomer3 third bulk 80% 0.920 LLDPE; 73 20% 0.923 LDPE

TABLE III-B provides an alternative to the multilayer film described inTABLE III-A. TABLE III-B percent of layer layer total film order namelayer function chemical identity thickness 1 second seal ionomer 10 2first seal-assist 70% 0.900 g/cc homo- 30 geneous Et/alpha-olefin; 30%0.88 g/cc homo- geneous plastomer 3 third bulk 80% 0.920 LLDPE; 60 20%0.923 LDPE

In FIG. 4, multilayer film 46 comprises outer sealant layer 48,seal-assist layer 50, tie layer 52, and thermoforming and heat-resistantlayer 54. Preferably, multilayer film 46 has a total thickness of fromabout 0.5 to 8 mils; more preferably, 0.75 to 6 mils, and still morepreferably about 1.5 to 5 mils. Preferably, outer sealant layer 48 iscomposed of an ionomer resin; preferably, seal-assist layer 50 iscomposed of a substantially homogeneous composition comprising ahomogeneous ethylene/alpha-olefin copolymer, a homogeneousethylene/alpha-olefin copolymer plastomer, and low density polyethylene;preferably, tie layer 52 comprises an anhydride-modified grafted linearlow density polyethylene; and, preferably thermoforming andheat-resistant layer 54 is composed of polyamide. Table IV provides thestructural and compositional characteristics of multilayer film 46.TABLE IV percent of layer layer total film order name layer functionchemical identity thickness 1 second outer sealant ionomer 8 2 firstseal-assist 55% 0.915 g/cc homo- 55 geneous ethylene/ alpha-olefincopolymer; 35% 0.23 g/cc homogeneous ethylene/alpha- olefin copolymerplastomer; 10% LDPE 3 fourth tie anhydride-modified, 7 grafted LLDPE 4third thermo- nylon 6 30 forming & heat-resistance

In FIG. 5, multilayer film 56 comprises: outer sealant layer 58;seal-assist layer 60; tie layer 62; thermoforming and abuse layer 64; O₂barrier layer 66; thermoforming and abuse layer 68; tie layer 70;thermoforming and abuse layer 72; and thermoforming and heat-resistantlayer 74. Preferably, multilayer film 56 has a total thickness of fromabout 0.5 to 8 mils; more preferably, 0.75 to 6 mils, and still morepreferably from about 1.5 to 5 mils. Preferably, outer sealant layer 58is composed of an ionomer resin; preferably, seal-assist layer 60 iscomposed of a substantially homogeneous composition comprising ahomogeneous ethylene/alpha-olefin copolymer, a homogeneousethylene/alpha-olefin copolymer plastomer, and low density polyethylene;preferably, tie layer 62 is composed of anhydride-modified graftedlinear low density polyethylene; preferably, thermoforming and abuselayer 64 is composed of polyamide; preferably, O₂ barrier layer 66 iscomposed of ethylene/vinyl alcohol copolymer; preferably, thermoformingand abuse layer 68 is composed of polyamide; preferably tie layer 70 iscomposed of anhydride-modified grafted linear low density polyethylene;preferably, thermoforming and abuse layer 72 is composed ofethylene/propylene copolymer; and preferably, thermoforming andheat-resistant layer 74 is composed of propylene homopolymer. Table V-Aprovides the structural and compositional characteristics of multilayerfilm 56. TABLE V-A percent of layer layer total film order name layerfunction chemical identity thickness 1 second heat seal ionomer 8 2first seal-assist 55% 0.915 g/cc homo- 20 geneous ethylene/alpha-olefin; 35% 0.87 g/cc homogeneous ethylene/alpha- olefinplastomer; 10% 0.923 g/cc LDPE 3 fourth tie anhydride-modified, 10grafted LLDPE 4 fifth thermoforming blend of 85% nylon 6 6 & abuse & 15%amorphous nylon 5 third oxygen EVOH 6 barrier 6 sixth thermoformingblend of 85% nylon 6 6 & abuse & 15% amorphous nylon 7 eighth tieanhydride-modified 7 grafted LLDPE 8 ninth thermoformingethylene/propylene 22 & abuse copolymer 9 seventh heat-resis- propylenehomopolymer 15 tance, & thermoforming

TABLE V-B provides an alternative to the multilayer film described inTABLE V-A. TABLE V-B percent of layer layer total film order name layerfunction chemical identity thickness 1 first outer seal 65% 0.900 g/cchomo- 10 geneous Et/alpha- olefin; 35% 0.87 g/cc homogeneousethylene/alpha- olefin plastomer 2 second seal-assist 65% 0.915 g/cchomo- 20 geneous ethylene/ alpha-olefin; 35% 0.87 g/cc homogeneousethylene/alpha- olefin plastomer; 3 sixth tie anhydride-modified, 10grafted LLDPE 4 fourth thermoforming blend of 85% nylon 6 6 & abuse &15% amorphous nylon 5 third O₂ barrier EVOH 6 6 fifth thermoforming 85%nylon 6; 6 & abuse 15% amorphous nylon 7 eighth tie anhydride-modified 7grafted LLDPE 8 ninth thermoforming ethylene/propylene 25 & abusecopolymer 9 seventh heat-resis- propylene homopolymer 10 tance, &thermoforming

In FIG. 6, multilayer film 76 comprises: outer sealant layer 78;seal-assist layer 80; tie layer 82; thermoforming, abuse, andultraviolet-protection layer 84; O₂ barrier layer 86; thermoforming,abuse, and ultraviolet-protection layer 88; tie layer 90; thermoforming,abuse, and heat-resistant layer 92. Preferably, multilayer film 76 has atotal thickness of from about 0.5 to 15 mils; more preferably, 1 to 10mils, and still more preferably from about 2 to 8 mils. Preferably,outer sealant layer 78 is composed of an ionomer resin; preferably,seal-assist layer 80 is composed of a substantially homogeneouscomposition comprising a homogeneous ethylene/alpha-olefin copolymer, ahomogeneous ethylene/alpha-olefin copolymer plastomer, and low densitypolyethylene; preferably, tie layer 82 is composed of anhydride-modifiedgrafted linear low density polyethylene; preferably, thermoforming,abuse, and ultraviolet-protection layer 84 is composed of polyamide;preferably, O₂ barrier layer 86 is composed of ethylene/vinyl alcoholcopolymer; preferably, thermoforming, abuse, and ultraviolet-protectionlayer 88 is composed of polyamide; preferably tie layer 90 is composedof anhydride-modified grafted low density polyethylene; preferably,thermoforming, abuse, and heat-resistant layer 92 is composed ofethylene/propylene copolymer.

Table VI provides the structural and compositional characteristics ofmultilayer film 76. TABLE VI percent of layer layer total film ordername layer function chemical identity thickness 1 second heat sealionomer 8 2 first seal-assist 55% 0.915 g/cc homo- 20 geneous ethylene/alpha-olefin; 35% 0.87 g/cc homogeneous ethylene/alpha- olefinplastomer; 10% 0.923 g/cc LDPE 3 seventh tie anhydride-modified, 11grafted LLDPE 4 fifth thermoforming, blend of 85% nylon 6 6 abuse, & uv& 15% amorphous nylon protection 5 third oxygen EVOH 6 barrier 6 sixththermoforming, blend of 85% nylon 6 6 abuse, & uv & 15% amorphous nylonprotection 7 eighth tie anhydride-modified 35 grafted LDPE 8 fourththermoforming, nylon 6 8 abuse, and heat-resistance

In FIG. 7, multilayer film 94 comprises: sealant layer 96; tie layer 98;thermoforming, abuse, and ultraviolet-protection layer 100; O₂ barrierlayer 102; thermoforming, abuse, and ultraviolet-protection layer 104;tie layer 106; and thermoforming, abuse, and heat-resistant layer 108.Preferably, multilayer film 94 has a total thickness of from about 0.5to 15 mils; more preferably, 1 to 10 mils, and still more preferablyfrom about 2 to 8 mils. Preferably, sealant layer 96 is composed of asubstantially homogeneous composition comprising a homogeneousethylene/alpha-olefin copolymer, a homogeneous ethylene/alpha-olefincopolymer plastomer, and low density polyethylene; preferably, tie layer98 is composed of anhydride-modified grafted linear low densitypolyethylene; preferably, thermoforming, abuse, andultraviolet-protection layer 100 is composed of polyamide; preferably,O₂ barrier layer 102 is composed of ethylene/vinyl alcohol copolymer;preferably, thermoforming, abuse, and ultraviolet-protection layer 104is composed of polyamide; preferably, tie layer 106 is composed ofanhydride-modified grafted ethylene/vinyl acetate copolymer; preferably,thermoforming, abuse, and heat-resistant layer 108 is composed ofpolyamide.

Table VII provides the structural and compositional characteristics ofmultilayer film 94. TABLE VII percent of layer layer total film ordername layer function chemical identity thickness 1 first seal 55% 0.900g/cc homo- 25 geneous ethylene/ alpha-olefin; 35% 0.86 g/cc EPDMelastomer; 10% 0.923 g/cc LDPE 2 third tie anhydride-modified, 12grafted LLDPE 3 fourth thermoforming, 85% nylon 6; 10 abuse, & uv 15%amorphous nylon protection 4 second O₂ barrier EVOH 8 5 sixththermoforming, 85% nylon 6; 10 abuse, & uv 15% amorphous nylonprotection 6 seventh tie anhydride-modified 25 grafted EVA 7 fourththermoforming, nylon 6 10 abuse, and heat-resistance

In FIG. 8, multilayer film 110 comprises: outer sealant layer 112;seal-assist layer 114; tie layer 116; thermoforming and abuse layer 118;tie layer 120; thermoforming and abuse layer 122; tie layer 124; and,thermoforming, abuse, and heat-resistant layer 126. Preferably,multilayer film 110 has a total thickness of from about 0.5 to 15 mils;more preferably, 1 to 10 mils, and still more preferably from about 2 to8 mils. Preferably, outer sealant layer 112 is composed of an ionomerresin; preferably, seal-assist layer 114 is composed of a substantiallyhomogeneous composition comprising a homogeneous ethylene/alpha-olefincopolymer, a homogeneous ethylene/alpha-olefin copolymer plastomer, andlow density polyethylene; preferably, tie layer 116 is composed ofhomogeneous ethylene/alpha-olefin copolymer and anhydride-modifiedgrafted low density polyethylene; preferably, thermoforming and abuselayer 118 is composed of polyamide; preferably, tie layer 120 iscomposed of anhydride-grafted ethylene/vinyl acetate copolymer;preferably, thermoforming and abuse layer 122 is composed of polyamide;preferably tie layer 124 is composed of anhydride-modified graftedethylene/vinyl acetate copolymer; preferably, thermoforming, abuse, andheat-resistant layer 126 is composed of polyamide.

Table VIII provides the structural and compositional characteristics ofmultilayer film 110. TABLE VIII percent of layer layer total film ordername layer function chemical identity thickness 1 second seal ionomer 82 first seal-assist 55% 0.915 g/cc homo- 27 geneous ethylene/alpha-olefin; 35% 0.87 g/cc homogeneous ethylene/alpha-olefin plastomer;10% 0.923 g/cc LDPE 3 seventh tie 80% 0.915 g/cc 12 homogeneousethylene/alpha olefin copolymer; 20% anhydride- modified LDPE 4 fifththermoforming nylon 6 10 & abuse 5 third tie anhydride-grafted EVA 11 6sixth thermoforming nylon 6 10 & abuse 7 eighth tie anhydride-graftedEVA 12 8 fourth thermoforming, copolymer of 85% 10 abuse, & nylon 6/heat-resistance 15% nylon 66

In FIG. 9, multilayer film 128 comprises: outer sealant and food-contactlayer 130; seal-assist layer 132; tie layer 134; memory layer 136; tielayer 138; and non-contact seal layer 140. Preferably, multilayer film128 has a total thickness of from about 0.5 to 15 mils; more preferably,1 to 10 mils, and still more preferably from about 2 to 8 mils.Preferably, outer sealant and food-contact layer 130 is composed of anionomer resin; preferably, seal-assist layer 132 is composed of asubstantially homogeneous composition comprising a homogeneousethylene/alpha-olefin copolymer and a homogeneous ethylene/alpha-olefincopolymer plastomer; preferably, tie layer 134 is composed ofanhydride-modified grafted linear low density polyethylene; preferably,memory layer 136 is composed of polyamide; preferably, tie layer 138 iscomposed of anhydride-grafted linear low density polyethylene;preferably, non-contact sealant layer 140 is composed of a substantiallyhomogeneous composition comprising a homogeneous ethylene/alpha-olefincopolymer and a homogeneous ethylene/alpha-olefin copolymer plastomer.

Table IX provides the structural and compositional characteristics ofmultilayer film 128. TABLE IX percent of layer layer total film ordername layer function chemical identity thickness 1 first seal & foodionomer 8 contact 2 third seal-assist 65% 0.915 g/cc homo- 17 geneousethylene/ alpha-olefin copolymer; 35% 0.87 g/cc homogeneous ethylene/alpha-olefin plastomer 3 fifth tie anhydride-grafted 15 LLDPE 4 fourthmemory nylon 6 25 5 sixth tie anhydride-grafted 15 LLDPE 6 secondnon-contact 65% 0.915 g/cc homo- 20 seal geneous ethylene/ alpha-olefin;35% 0.87 g/cc homo- geneous ethylene/ alpha-olefin plastomer

The films according to the present invention are suited to manydifferent forms of packaging applications, such as bags, casings,forming stock (suitable for thermoforming), and lidstock, including bothheat-shrinkable as well as non-heat-shrinkable films for all of theseapplications. However, the films illustrated in

Although in general the film and package according to the presentinvention can be used in the packaging of any product, the film andpackage of the present invention are especially advantageous for thepackaging of food products, especially food products packaged in: (a)thermoformed webs having a lidstock sealed thereto, especiallythermoformed packages containing meat products, the package being usedin a cook-in application; (b) bags, especially bags used in vacuumpackaging; (c) casings, especially casings used to package processedmeats, such as shirred casings, which can optionally also be used incook-in applications. Among the meat products which can be packaged inthe films and packages according to the present invention are poultry,pork, beef, lamb, goat, horse, and fish.

FIG. 10 illustrates one embodiment of a packaged product 142 of thepresent invention, the product being packaged in a casing closed by apair of clips 144 at each end thereof, with only one being illustratedin FIG. 10. Film 146, used to package the meat product therewithin, canbe, for example, multilayer film 128 illustrated in FIG. 9, discussed indetail above. In FIG. 10, the cooked meat product preferably comprisesprocessed poultry, processed beef, and/or processed pork.

FIG. 11 illustrates another embodiment of a packaged product 148,according to the present invention. The product, a cooked meat product,is packaged in a heat-sealed, heat-shrinkable bag, within which the meatproduct has been cooked. The package comprises multilayer film 150. InFIG. 11, the cooked meat product preferably comprises pork, in the formof a boneless ham.

FIG. 12 illustrates yet another embodiment of a packaged product 154,according to the present invention. The product, a cooked meat product,is packaged in a heat-sealed, thermoformed web having a lidstock websealed thereto, with the meat product being cooked within the sealedthermoformed package. The package comprises multilayer film 156, whichcan be, for example, multilayer film 76 illustrated in FIG. 6, ormultilayer film 56 illustrated in FIG. 5, both of which are discussed indetail above. In FIG. 11, the cooked meat product comprises poultry,more specifically, a boneless turkey breast product.

FIG. 13 illustrates yet another embodiment of a packaged product 158,according to the present invention. The product, a cooked meat product(e.g., hot dogs), is packaged in heat-sealed, thermoformed web 160having lidstock web 162 sealed thereto. Thermoformed web 160 can be, forexample, multilayer film 46 illustrated in FIG. 4, or multilayer film 56illustrated in FIG. 5, both of which are discussed in detail above.Lidstock 162 can be, for example, multilayer film 94 illustrated in FIG.7, or multilayer film 110 illustrated in FIG. 8, both of which arediscussed in detail above.

FIG. 14 illustrates a cross-sectional view of packaged product 158 ofFIG. 13, taken through section 14-14 of FIG. 14. FIG. 14 illustrateslidstock web 162 making up the top of the package, and thermoformed web160 making up the bottom and sides of the package, and seal 164 ofthermoformed web 160 to lidstock web 162, seal 164 being around the topof packaged product 158.

FIG. 15 represents an enlarged cross-sectional view of a seal 166 usedin the package according to the present invention. First film region 168is sealed to second film region 170 at seal 172. Seal 172 is produced byheating the first film region 168 and second film region 170 in order tocause the contacting portions of the films to simultaneously melt andflow together.

FIG. 16 represents an enlarged cross-sectional view of a lap-sealed filmtube 172. Film 174 is formed into a tube, and lap seal 176 is formedalong the length of the tube. Such seals as seal 176 are termed “lapseals” because the film is lapped over itself, with the outside surface178 of the film being sealed to the inside surface 180 of the film, atlap seal 176.

FIG. 17 represents an enlarged cross-sectional view of a package 182,such as a cross-section of a vertical form fill and seal package, havinga first film 184 sealed to second film 186 via a pair of fin seals 188.Seals such as 188 are termed “fin seals” because, unlike lap seals, theyprotrude from the package, much as the fin of a fish protrudes from itsbody. As can be seen, both of the fin seals 188 of package 182 are aseal of inside surface 190 of first film 184 to inside surface 192 ofsecond film 186.

FIG. 18 illustrates a schematic view of a process useful in making filmsaccording the present invention. Although for the sake of simplicityonly one extruder 194 is illustrated in FIG. 18, there are preferably atleast two extruders, and more preferably, at least three extruders. Thatis, preferably at least one extruder, and more preferably two extruders,supply molten polymer to coextrusion die 196 for the formation of, forexample, outer layers 40 and 44 of the three-layer film illustrated inFIG. 3; and at least one additional extruder to supply molten polymer tocoextrusion die 196 for the formation of, for example, core layer 42 inthe three-layer film illustrated in FIG. 3. Each of the extruders issupplied with polymer pellets suitable for the formation of therespective layer it is extruding. The extruders subject the polymerpellets to sufficient pressure and heat to melt the polymer and therebyprepare it for extrusion through a die.

Taking extruder 194 as an example, each of the extruders is preferablyequipped with a screen pack 198, a breaker plate 200, and a plurality ofheaters 202. Each of the coextruded film layers is extruded betweenmandrel 204 and die 196, and the extrudate is cooled by cool air flowingfrom air ring 206. The resulting blown bubble 207 is thereafter guidedinto a collapsed configuration by nip rolls 208, via guide rolls 210.The collapsed tube is optionally passed over treater bar 212, and isthereafter passed over idler rolls 214, and around dancer roll 216 whichimparts tension control to collapsed tube 218, after which the collapsedtube is wound into roll 220 via winding mechanism 222.

FIG. 19 illustrates a schematic view of a cast coextrusion process offilm manufacture, in which various polymeric formulations are suppliedto slot-shaped die 224 from a plurality (preferably, from 3 to 10) ofextruders 226, only one of which is illustrated in FIG. 7. The number ofextruders 226 is at least as great as the number of different chemicalcompositions present in the various layers of the multilayer film, butcan be fewer than the number of layers of the film in the event that astream from an extruder is split to form two different film layers.Typically, the extruders are single screw extruders which convertpolymer granules or pellets into a continuous uniform melt underelevated temperatures and pressure. The molten masses formed within thevarious extruders are converged into a plurality of layers in a streamwhich is forced into flat laminar flow for the width of the slot of die224, and thereafter forced through the slot of die 224, to yield thedesired shape. After passing through the slot of die 224, melt 228passes downward vertically and tangentially contacts chill roll 230which quenches melt 228, forming multilayer film 232 thereon. Chill roll230 is highly polished and water-cooled, and rotates with melt 228 atthe speed at which melt 228, and film 232, are drawn forward. Film 232then leaves the surface of chill roll 230, and thereafter may contactthe surface of from one to three supplemental chill rolls 234 (only onesupplemental chill roll 234 is illustrated in FIG. 19), which are alsowater-cooled and highly polished, and which further cool multilayer film232, which thereafter passes over guide rolls 236 and through the nip ofnip rolls 238. Film 232 is thereafter directed over guide rolls 240 and242. Thereafter, film 232 passes between a nip between rubber nip roll244 and stainless steel nip roll 246, and is then wound up into roll 248by winder 250. The width of the cast film web is determined by the dieslot width. The thickness of film 232 is determined by the relationshipbetween the output of extruder 226 and the takeaway speed of the film232.

In FIG. 20, substrate film 252, supplied from roll 254, is directed ontochill roll 230 and coated with molten coating 256 passing verticallydownward from slot die 224 towards chill roll 230. Coating 256 is cooledby chill roll 230, the heat from coating 256 passing through substratefilm 252 and into chill roll 230, to result in coated substrate 258.Furthermore, if additional downstream chill rolls are present, such aschill roll 234, further cooling can be effected by direct contact ofcoating 256 with the smooth surface of the chill roll, i.e., withoutsubstrate film 252 between coating 256 and the chill roll. Subsequentdownstream processing of coated substrate 258 is the same as describedin FIG. 19.

FIG. 21 illustrates yet another process which can be used to make filmsin accord with the present invention. The process of FIG. 21 is asgenerally disclosed in U.S. Pat. No. 4,287,151, to ESAKOV, et. al.,hereby incorporated by reference thereto, in its entirety.

In the process illustrated in FIG. 21, tubular extrudate 260 wasdownwardly formed from die 262, the tubular extrudate enclosing airmandrel 264. At approximately this point in the process, an exteriorcooling means, in the form of water ring 266, encircles tubularextrudate 260. Water ring 266 in the shape of a circular tray, had anopening therethrough, the opening having a diameter slightly larger thanthat of tubular extrudate 260. A constant flow of water, at about 50°F., is supplied to water ring 266. The overflow from the water ringprovided an annular film of water on the outer surface of extrudate 260.The water fell downwardly around the entire outer periphery of extrudate260, thereby cooling extrudate 260. The film of water is collected byreceptacle 268. Water was the preferred cooling medium because its heatcapacity and heat transfer characteristics are such as to cool extrudate260 more rapidly than a chilled gas would have. However, as analternative to water ring 266, a fine spray of cooled water could havebeen directed against the exterior surface of the extrudate 260. Incombination, air mandrel 264 and water ring 266 serve as the means tocool and solidify extrudate 260. In some instances, depending upon thepolymer being extruded and upon the wall thickness of extrudate 260,either the interior or exterior cooling could be eliminated, because onecooling means alone would be sufficient to solidify the interior tubewall before reaching support plug 270. Once solidified, extrudate 272 iscollapsed by rolls 274, to form a solidified lay flat tubing 276.

The polymer components used to fabricate multilayer films according tothe present invention may also contain appropriate amounts of otheradditives normally included in such compositions. These include slipagents such as talc, antioxidants, fillers, dyes, pigments and dyes,radiation stabilizers, antistatic agents, supplemental elastomers, andthe like additives known to those of skill in the art of packagingfilms.

Although the multilayer film of the present invention is preferably notirradiated, optionally the film may be irradiated. In the irradiationprocess, the film is subjected the film to an energetic radiationtreatment, such as corona discharge, plasma, flame, ultraviolet, X-ray,gamma ray, beta ray, and high energy electron treatment, which inducecross-linking between molecules of the irradiated material. Theirradiation of polymeric films is disclosed in U.S. Pat. No. 4,064,296,to BORNSTEIN, et. al., which is hereby incorporated in its entirety, byreference thereto. BORNSTEIN, et. al. discloses the use of ionizingradiation for crosslinking the polymer present in the film.

Radiation dosages are referred to herein in terms of the radiation unit“RAD”, with one million RADS, also known as a megarad, being designatedas “MR”. A suitable radiation dosage of high energy electrons is in therange of up to about 12 MR, more preferably about 2 to about 9 MR, andstill more preferably, about 3 MR. Preferably, irradiation is carriedout by an electron accelerator and the dosage level is determined bystandard dosimetry methods.

As used herein, the phrases “corona treatment” and “corona dischargetreatment” refer to subjecting the surfaces of thermoplastic materials,such as polyolefins, to corona discharge, i.e., the ionization of a gassuch as air in close proximity to a film surface, the ionizationinitiated by a high voltage passed through a nearby electrode, andcausing oxidation and other changes to the film surface.

Corona treatment of polymeric materials is disclosed in U.S. Pat. No.4,120,716, to BONET, issued Oct. 17, 1978, herein incorporated in itsentirety by reference thereto, discloses improved adherencecharacteristics of the surface of polyethylene by corona treatment, tooxidize the polyethylene surface. U.S. Pat. No. 4,879,430, to HOFFMAN,also hereby incorporated in its entirety by reference thereto, disclosesthe use of corona discharge for the treatment of plastic webs for use inmeat cook-in packaging, with the corona treatment of the inside surfaceof the web to increase the adhesion of the meat to the adhesion of themeat to the proteinaceous material.

Although corona treatment is a preferred treatment of the multilayerfilm of the present invention, plasma treatment of the film may also beused.

Films such as those illustrated in FIGS. 4, 5, 6, 7, and 8, are especialsuitable for use as forming web or lidstock in thermoforming typepackaging operations. Regarding films designed for such use, preferably,the lidstock is a multilayer film comprising the same number of layersand relative layer percentages (thicknesses), differing only in that ithas a total thickness of about 50% the total thickness of the formingweb.

Both a forming web and a non-forming web can be fed from two separaterolls, with the forming web being fed from a roll mounted on the bed ofthe machine for forming the package “pocket,” i.e., the product cavity.The non-forming (lidstock) web is usually fed from a top-mounted arborfor completing the airtight top seal of the package. Each web has itsmeat-contact/sealant surface oriented towards the other, so that at thetime of sealing, the sealant surfaces face one another. The forming webis indexed forward by transport chains, and the previously sealedpackage pulls the upper non-forming web along with the bottom web as themachine indexes.

The first step in the packaging process is the formation of the productcavity in the forming web. The cavity forming is a three-step process:(1) index; (2) heat; (3) form. While one cavity is being formed, the webfor the next cavity is undergoing preheating before being indexed overthe pocket-forming die. To accomplish this, the forming web is heatedfrom 70° C. to 80° C. by being pressed against a contact-type heater bymeans of vacuum. The forming web is then formed by use of compressed airor vacuum, or both. Compressed air pushes the heated film into the diecavity from above and, in turn, vacuum pressure pulls the film intoshape from within the die. A plug is used to assist the movement of theheated film into the die cavity.

After forming, the transport chains carry the empty pocket to theloading station where the product is either hand loaded or pumped intothe cavity. The transport chains then carry the loaded product to thevacuum and sealing station.

The sealing process is a series of operations occurring simultaneouslyor with a slight overlap. Once the top film is in place over the filledcavity, the sealing chamber closes. Package air is exhausted between thetop and bottom films. The upper chamber, or lid, employs a heated sealplate set at from 150° C. to 170° C., which bonds the non-forming weband the forming web together.

The vacuum in the seal die balances chamber pressures, and ensures thatno air is trapped between the product and the forming web. The sealingdiaphragms, empty of air, are now filled with compressed air. Thispresses the heated sealing plate against the upper film, compressing theheat-sealable surfaces of the two webs between the sealing plate and theT-rubber sealing gasket. The heat and pressure of the sealing platecauses the two surfaces of the films to bond together, sealing theproduct in a vacuum environment. Approximately 0.4 to 0.5 seconds aftersealing ends, the upper and lower chambers are vented to the atmosphere,causing the top and bottom films to collapse around the product. Now,the sealing diaphragms evacuate and the sealing plate moves back up.Outside air rushes into the chambers. When the air pressures areequalized, the die bottom can move down, allowing the package to beindexed out of the seal station.

The sealed package is then separated from the web by way of a contourknife system. The packages are conveyed through a hot water (205° F.)shrink tunnel. The packages are placed on racks and cooked in a highhumidity oven. The product is then chilled and available for shipping orfor further processing, which may involve stripping the package off ofthe product.

The invention is illustrated by the following examples, which areprovided for the purpose of representation, and are not to be construedas limiting the scope of the invention. Unless stated otherwise, allpercentages, parts, etc. are by weight, and all density figures are ing/cc.

EXAMPLE 1

A nine-layer multilayer film was produced in accordance with the processas illustrated in FIG. 21, described above.

Eight conventional single-screw extruders were employed to melt and pumpvarious resins to a distribution block or adapter and then an annularcoextrusion die. The EVOH layer was processed at temperatures of fromabout 350° F. and 450° F. The LLDPE, homogeneous ethylene/alpha-oleincopolymer, elastomer and/or plastomer were extruded at a temperature offrom about 400° F. to 500° F. The nylon-containing layers were processedat a temperature of from about 450° F. to 550° F. Tie layers, which wereanhydride-grafted resins, were processed at temperatures of from about420° F. to 460° F., regardless of the composition of the base resin, inorder that the anhydride functionalities reacted to allow the tie layerto provide the desired compatibility. The melt distribution system anddie were designed to produce uniform thickness distribution around thecircumference of the die, for all nine layers.

The flattened tape 10″ was passed through pinch rollers, heated in a hotwater bath or by a hot air oven, and expanded by inflating the tube withhigh pressure air in what is well known in the art as the “trappedbubble technique.” By this means, a thermoplastic film of desiredthickness was produced. The oriented thermoplastic film, in the form oflay flat tubing 10″′, which was then cut lengthwise, i.e., along bothedge creases, to form two separate film sheets, each of which werethereafter wound up onto two substantially identical, but separate,rolls. Thereafter, each of the rolls of film was resized on a slitter,to produce a width and diameter suitable for a horizontal packagingmachine, such as a TIROMAT™ thermoforming packaging machine, MULTIVAC™thermoforming packaging machine, PIONEER™ thermoforming packagingmachine, or MAHAFFEY HARDER™ thermoforming packaging machine. The filmwas used primarily as the forming film of the machine, but it could alsobe used as a non-forming film.

The film was suitable for the packaging of food products such as freshand processed poultry, fresh and processed red meat, fresh and processedfish, and fresh and processed pork, cheese; more particularly, hot dogs,bacon, summer sausage, block cheese, and cheese sticks. The foodspackaged in the film could be precooked, marinated, preseasoned,breaded, etc.

The film was suitable for use as a forming film and/or a non-formingfilm for cook-in applications, where the sealant layer is corona orirradiation treated so as to provide meat adhesion to the proteinextracted meat emulsion mixture typical of cooled ham, turkey breast,and other further processed meat products.

In a corona treated state of from about 36 to 60 dyne/cm sec, theoxidized surface of the film increases the compatibility of the surfacesealant layer, so as to provide even greater seal strength between thesurface layer blend and sealants which are generally recognized as beingincompatible with ionomer resins, such as SURLYN 1601 ™ ionomer resin,SURLYN 1705 ™ ionomer resin, and SURLYN 1650 ™ ionomer resin. Becausethe outer heat-resistant forming layer is composed of polypropylenehomopolymer, the treated outer sealant layer does not cause excessiveblocking to occur.

Table V-B, above, provides the structural and compositionalcharacteristics of the nine-layer film produced as described above. InTable V-B, the numerals indicating the “layer order” correspond with theposition of the layers relative to one another, with layer 1 being theinside layer of the tube, and layer 6 being the outside layer of thetube. Layer 2 is in direct contact with layers 1 and 3, layer 3 indirect contact with layers 2 and 4, and so on. In contrast, the “layername” designates the various layers as “first”, “second”, etc., theselayer names corresponding with the detailed description of therespective Figures, as discussed above, and the names of the layersrecited in the claims, as set forth below.

Three films were produced in accord with Example 1, the films differingonly in total thickness (same relative proportion to each layer), thetotal thicknesses being about 2.5 mils, about 3 mils, and about 3.5mils. The various resins in the layers were as follows: Layer #1 is ablend of (a) 65 weight percent EXACT 3027 ™ homogeneousethylene/alpha-olefin 0.900 g/cc resin, obtained from the Exxon ChemicalCompany, of Baytown, Tex., and (b) 35 weight percent TAFMER PO 480 ™0.87 g/cc homogeneous ethylene/alpha-olefin copolymer plastomer resin,produced by Mitsui Sekka, of Japan, and obtainable from the MitsuiPetrochemicals (America), Ltd., of N.Y., N.Y. Layer #2 was a blend of(a) 55% ECD 301 ™ 0.915 g/cc homogeneous ethylene/alpha-olefin copolymerresin, also obtained from the Exxon Chemical Company, (b) 35 weightpercent TAFMER PO 480 ™ homogeneous ethylene/alpha-olefin copolymerplastomer resin, and (c) 10 weight percent LD 200.48 ™ LDPE resin, alsoobtained from the Exxon Chemical Company. Layer #3 and Layer #7 wereeach TYMOR 1203 ™ LLDPE-based anhydride grafted copolymer, obtained fromMorton International Inc., of Chicago, Ill. Layer #4 and Layer #6 wereeach a blend of (a) 85 weight percent ULTRAMID B35 ™ polyamide resin,obtained from BASF Corporation of Charlotte, N.C., and (b) 15 weightpercent GRIVORY G 21 ™ amorphous polyamide resin, obtained fromEMS-American Grilon, Inc. of Sumter, S.C. Layer #5 was SOARNOL E/T™polymerized ethylene vinyl alcohol copolymer resin (saponified ethylenevinyl acetate copolymer) produced by Nippon Gohsei, and obtained fromMorton International Specialty Chemical Company, of Chicago, Ill. Layer#8 was ESCORENE PD 9012 ™ (heterogeneous) propylene/ethylene copolymerresin, also obtained from the Exxon Chemical Company. Layer #9 wasESCORENE PD 3445 ™ (heterogeneous) polypropylene homopolymer, alsoobtained from Exxon Chemical Company.

EXAMPLE 2

A nine-layer film was produced in a manner substantially as described inExample 1, except that the ionomer was processed at a temperature offrom about 400° F. to 500° F.

Table VI, above, provides the structural and compositionalcharacteristics of the nine-layer film produced in this Example.

The film of Table VI, i.e., according to Example 2, had a totalthickness of about 2 to 4 mils. The various resins in the layers were asfollows: Layer #1 was SURLYN 1650 ™ ethylene methacrylic acid copolymerresin, wherein the acid had been partially neutralized with a zinc base,such as zinc acetate. The SURLYN 1650 ™ ethylene methacrylic acidcopolymer resin was obtained from E.I. DuPont de Nemours, of Wilmington,Del. Layers #2, #3, #4, #5, #6, and #7 had the same chemical compositionas the same-numbered layers of the nine-layer film of Example 1.However, Layer #8 was BYNEL CXA 3095 ™ anhydride graft copolymer of anethylene vinyl acetate copolymer resin, obtained from E.I. DuPont deNemours. Layer #9 was ULTRAMID B35 polyamide resin, obtained from BASFCorporation of Charlotte, N.C.

After exiting the die, the film was processed as described in Example 1,above. The film of this Example can be used to package products,especially the food products as described in Example 1.

The film of this Example used a relatively thin (0.2 mils) SURLYN™ionomer “cap layer”, and hence is compatible with, i.e., readilysealable to, other films having an outer ionomer layer. However, beforethe instant invention it has been believed by those of skill in the artthat sealant layers must comprise sufficient thickness so as to provideadequate material to flow around surface contamination such as oils,fats, and particulate matter, and surface imperfections in the exteriorsurface of the opposing sealing layer. If sufficient material is notpresent, seals through the contaminated area are frequently too weak tosurvive abuse and stresses during commercial distribution of the productpackaged in the film.

The film of Example 2 utilized, in its “seal-assist layer”, i.e., layer#2, almost the same blend used in the seal layer, i.e., layer #1, in thefilm of Example 1. In the film of Example 2, the seal-assist layerprovided over 70 percent of the required thickness needed forsealability through contamination.

Furthermore, the film of Example 2, because of its outer nylonheat-resistant and abuse-resistant layer, i.e. Layer #9, could be usedequally well as both a thermoforming and non-thermoforming film, on suchhigh speed packaging machines used in the high speed packaging of, forexample, hot dogs.

Finally, because the film of Example 2 utilizes a zinc SURLYN ™ ionomerresin sealant layer, it can be used for cook-in meat applications, withor without the addition of corona or irradiation treatment (i.e.,oxidation) of the sealant layer.

EXAMPLE 3

The films produced in Examples 1 and 2 can be produced by the cast filmprocess illustrated in FIG. 7. Six conventional single-screw extrudersare employed to melt and pump the various resins through the injectionblock or manifold slot die system. The EVA-containing andEVOH-containing layers are extruded at a temperature of from about 350°F. to 450° F., and the LLDPE-containing layers are extruded at atemperature of from about 400° F. to 500° F. The nylon-containing layersare extruded at 450° F. to 550° F. The melt system and die are designedwith flow channels to produce uniform distribution, across the width ofthe die, for all 7 layers.

Upon extrusion, the molten 7-layer web drops onto a water cooled chillroll having a temperature controlled to 40° F. to 60° F., which quicklybrings the molten web to room temperature, or below room temperature, sothat crystallization is minimized. This roll has internal spirally woundchannels that direct the water flow beneath the outer shell to providegood heat transfer characteristics. The web is “pinned” to the chillroll with an air knife or electrostatic pinning device commonly used incast film production.

The completed cast web is then wound into a roll and later resized to awidth suitable for a horizontal packaging machine, such as a Multivacthermoforming packaging machine. The roll of film is used as the formingweb in the thermoforming packaging machine.

EXAMPLE 4

A seven-layer film is produced by an upward blown coextrusion process,in which seven conventional, single-screw extruders are used to delivermelt and pump various polymer resins to a distribution manifold oradapter, which subsequently flows into distribution channels within anannular die.

FIG. 3 illustrates a schematic view of a process for making theseven-layer film in accordance with the present invention. Although forthe sake of simplicity only one extruder 20 is illustrated in FIG. 3,there are preferably at least 2 extruders, and more preferably, at leastthree extruders. That is, preferably at least one extruder, and morepreferably two extruders, supply molten polymer to coextrusion die 21for the formation of, for example, outer layers 11 and 13 as illustratedin FIG. 1, and at least one additional extruder supplied molten polymerto coextrusion die 21 for the formation of, for example, core layer 12as illustrated in FIG. 1. Each of the extruders is supplied with polymerpellets suitable for the formation of the respective layer it isextruding. The extruders subject the polymer pellets to sufficientpressure and heat to melt the polymer and thereby prepare it forextrusion through a die.

Taking extruder 20 as an example, each of the extruders is preferablyequipped with a screen pack 22, a breaker plate 23, and a plurality ofheaters 24. Each of the coextruded film layers is extruded betweenmandrel 25 and die 21, and the extrudate is cooled by cool air flowingfrom air ring 26. The resulting blown bubble is thereafter guided into acollapsed configuration by nip rolls 29, via guide rolls 28. Thecollapsed tube is optionally passed over treater bar 30, and isthereafter passed over idler rolls 31, and around dancer roll 32 whichimparts tension control to collapsed tube 33, after which the collapsedtube is wound into roll 34 via winding mechanism 35.

Table VII, above, describes the seven-layer blown, coextruded filmproduced according to this Example. This seven-layer film is useful insubstantially the same applications as described for the films ofExamples 1 and 2. In the film of Table VII, produced according to thisExample, the following is the identity of the various resins used ineach of the seven layers. Layer #1 is a blend of: (a) 65 weight percentEXACT 3027 ™ homogeneous ethylene/alpha-olefin 0.900 g/cc resin,obtained from the Exxon Chemical Company, of Baytown, Tex., and (b) 35weight percent Vistalon™ ethylene-propylene-diene terpolymer resin(“EPDM”, also known as ethylene-propylene rubber), also obtainable fromthe Exxon Chemical Company. Layer #2 is BYNEL CXA 4125 ™anhydride-grafted LLDPE resin, obtainable from E.I. Dupont de Nemours,of Wilmington, Del. Layer #3 and Layer #5 are each a blend of (a) 80weight percent CAPRON 1539 ™ polyamide resin, obtainable from the AlliedSignal Inc., of Morristown, N.J., and (b) 20 weight percent SELAR PA3426 ™ amorphous polyamide, also obtainable from E.I. DuPont de Nemours.Layer #4 is EVAL E101 ™ ethylene vinyl alcohol copolymer resin, i.e., a38 mole percent ethylene/vinyl alcohol copolymer, which is produced anddistributed by the Eval Co. of America, of Lisle, Ill. Layer #6 isPLEXAR 107 ™ anhydride modified EVA resin, obtainable from QuantumChemical Company, of Pittsburgh, Penn. Layer #7 is CAPRON 8207 ™polyamide resin, also obtainable from the Allied Signal Inc.

EXAMPLE 5

An eight-layer film is produced by an upward-blown coextrusion process,in the manner as set forth in Example 4. Table VIII, above, provides thephysical and chemical characteristics of this film. In the film producedaccording to this example, as set forth in Table VIII, above, theindividual film layers were composed of the following specifiedpolymers. Layer #1 is SURLYN 1601 ™ ionomer resin, obtainable from E.I.DuPont de Nemours. Layer #2 is a blend of: (a) 55 weight percent ECD 301™ 0.915 g/cc homogeneous ethylene/alpha-olefin resin, obtainable fromthe Exxon Chemical Company, (b) 35 weight percent EXACT SLP 9042 ™homogeneous ethylene/alpha-olefin copolymer resin, also obtainable fromthe Exxon Chemical Company, and (c) 10 weight percent PETROTHENE NA 345™ 0.923 LDPE resin, obtained from the Quantum Chemical Company. Layer #3is a blend of 80 weight percent ECD 301 ™ 0.915 g/cc homogeneousethylene/alpha-olefin resin, obtained from the Exxon Chemical Company,and 20 weight percent TYMOR 1N05 ™ anhydride grafted LDPE resin,obtained from the Morton International, Inc., of Chicago, Ill. Layers #4and #6 are ULTRAMID KR 4418 ™ polyamide resin, obtained from BASF, ofParsippany, N.J. Layers #5 and #7 are BYNEL CXA 3048 ™ anhydride graftedEVA resin, obtained from E.I. DuPont de Nemours. Layer #8 is UBE 5033B™polyamide resin, obtained from UBE Industries (America) Inc., of NewYork, N.Y., and distributed by Nichimen America, Inc., of N.Y., N.Y.

EXAMPLE 6

Using an adhesive, a three-layer film is laminated to a PVDC coated,biaxially-oriented heat-set polyester film. The three-layer,upwardly-blown coextruded film is produced according to Example 4, usingthree single-screw extruders. Otherwise, the process was carried out ina manner analogous to the process described above in Example 4.

Table X provides the structure and chemcial characteristics of thethree-layer film. TABLE X percent of layer layer total film order namelayer function chemical identity thickness 1 second seal ionomer 10 2first seal-assist 70% 0.900 g/cc homo- 30 geneous Et/alpha- olefin; 30%0.88 g/cc homo- geneous plastomer 3 third bulk 80% 0.920 LLDPE; 60 20%0.923 LDPE

Layer #1 is SURLYN 1705 ™ ionomer resin, obtainable from E.I. DuPont deNemours. Layer #2 is a blend of (a) 70 weight percent AFFINITY PM 1870 ™homogeneous ethylene/alpha-olefin copolymer resin, obtainable from theDow Chemical Company, and (b) 30 weight percent TAFMER PO 480 ™ 0.87g/cc homogeneous ethylene/alpha-olefin copolymer plastomer resin,produced by Mitsui Sekka, of Japan, and obtainable from the MitsuiPetrochemicals (America), Ltd., of N.Y., N.Y. Layer #3 is a blend of (a)80 weight percent DOWLEX 2045 ™ homogeneous ethylene/alpha-olefincopolymer resin, obtainable from the Dow Chemical Company, and (b) 20weight percent ESCORENE LD 200.48 ™ 0.923 g/cc polyethylene homopolymerresin, obtainable from the Exxon Chemical Company.

The blown, coextruded film had a total thickness of about 2 mils. Theblown, coextruded film was then adhesively laminated to a second film,resulting in a laminate. The second film was composed of MYLAR M44 ™PVDC-coated, biaxially-oriented, polyethylene terephthalate film,obtainable from E.I. DuPont de Nemours. The urethane adhesive used isADCOTE 545-E™ polyurethane adhesive, obtainable from MortonInternational, Inc., of Chicago, Ill. The resulting laminate has thecross-sectional structure: oriented polyethylene terephthalate, 0.48mils PVDC coating, 0.08 mils Urethane Adhesive, 0.12 mils Blend of LLDPEand LDPE,  1.2 mils blend of homogeneous ethylene/alpha-olefin 0.60 milscopolymer plastomer: ionomer, 0.20 mils

The film of Example 6 is suitable for both thermoforming applications aswell as non-thermoforming applications; for horizontal packagingmachines where the forming film utilizes a sealing layer of an ionomeror a blend of homogeneous ethylene/alpha-olefin copolymer withelastomer. The film of Example 6 can be used to package products in amanner as described for the films of Examples 1 and 2.

Forming films can be produced by the method of Example 6, i.e., adhesivelaminating by replacing the oriented, heat-set polyester film with anon-oriented, cast nylon film (typically at 2 mils and 4 mils thick)which can optionally be PVDC coated, in order to provide an 02 barrier.Typical of the coated laminating films which may be so used are: (a)DARTEK B 601 ™ PVDC coated cast polyamide film, distributed by E.I.DuPont de Nemours, of Wilmington, Del. and (b) CAPRAN 77 DFK™PVDC-coated, cast polyamide film, obtainable from the Allied Signal Inc.

EXAMPLE 7

Using an adhesive, a three-layer film is laminated to a PVDC coated,biaxially-oriented heat set polyester film. The three-layer,upwardly-blown coextruded film is produced according to Example 4,except that the process uses three single-screw extruders.

Table III, above, together with the accompanying description of FIG. 3,provides the structure and chemcial composition of the three-layer filmof Example 7. In the film as illustrated in Table III but being producedspecifically in accord with this Example, Layer #1 is SURLYN 1705 ™ionomer resin, obtainable from E.I. DuPont de Nemours. Layer #2 is ablend of (a) 70 weight percent AFFINITY PM 1870 ™ homogeneousethylene/alpha-olefin copolymer resin, obtainable from the Dow ChemicalCompany, and (b) 30 weight percent TAFMER PO 480 ™ 0.87 g/cc homogeneousethylene/alpha-olefin copolymer plastomer resin, produced by MitsuiSekka, of Japan, and obtainable from the Mitsui Petrochemicals(America), Ltd., of N.Y., N.Y. Layer #3 is a blend of (a) 80 weightpercent DOWLEX 2045 ™ homogeneous ethylene/alpha-olefin copolymer resin,obtainable from the Dow Chemical Company, and (b) 20 weight percentESCORENE LD 200.48 ™ 0.923 g/cc polyethylene homopolymer resin,obtainable from the Exxon Chemical Company.

The blown, coextruded film illustrated in FIG. 3 had a total thicknessof about 3 mils. The blown, coextruded film was then adhesivelylaminated to a second film, resulting in a laminate. The second film wascomposed of MYLAR M44 ™ PVDC-coated, biaxially-oriented, polyethyleneterephthalate film, obtainable from E.I. DuPont de Nemours. The urethaneadhesive used is ADCOTE 545-E™ polyurethane adhesive. The resultinglaminate has the cross-sectional structure: oriented polyethyleneterephthalate, 0.48 mils PVDC coating, 0.08 mils Urethane Adhesive, 0.12mils Blend of LLDPE and LDPE, 2.19 mils blend of homogeneousethylene/alpha-olefin 0.60 mils copolymer, ionomer, 0.20 mils

The film of Example 7 is suitable for both thermoforming applications aswell as non-thermoforming applications; for horizontal packagingmachines where the forming film utilizes a sealing layer of an ionomeror a blend of homogeneous ethylene/alpha-olefin copolymer withelastomer. The film of Example 7 can be used to package products in amanner as described for the films of Examples 1 and 2.

Although the film of Example 7 is very similar to the film of Example 8,the film of Example 8 has the advantage of further reducing thethickness of the ionomer outer sealant layer relative to the total filmthickness when compared to the film of Example 6.

EXAMPLE 8

A casing, used to package processed meat products, such as cooked ham,turkey rolls, sausage, bologna, etc., is produced using a 3 mil (totalthickness) upwardly-blown, coextruded multilayer film, the multilayerfilm being produced in a manner as set forth in Example 4, except that atotal of from 4 to 6 single-screw extruders can be used in the process.

Table IX, above, provides the physical and chemical characteristics ofthis multilayer film. More particularly, in the multilayer film producedaccording to this Example as generally illustrated and described in FIG.9 and Table IX, each of the layers is composed of the following specificpolymers. Layer #1 is SURLYN 1650 ™ ionomer resin, obtainable from E.I.DuPont de Nemours. Each of Layers #2 and #6 are a blend of: (a) 65weight percent ECD 301 ™ 0.915 g/cc ethylene/alpha-olefin copolymerresin, obtainable from the Exxon Chemical Company; and, (b) 35 weightpercent TAFMER P0 480 ™ 0.87 g/cc homogeneous ethylene/alpha-olefincopolymer plastomer resin, produced by Mitsui Sekka, of Japan, andobtainable from the Mitsui Petrochemicals (America), Ltd., of N.Y., N.Y.Layers #3 and #5 are TYMOR 1203 ™ anhydride modified grafted linear lowdensity polyethylene resin, obtainable from Morton InternationalSpecialty Chemical Company, of Chicago, Ill. Layer #4 is ULTRAMID B36 ™polyamide resin, obtainable from BASF Corporation.

Although the six-layer film which can be produced according to Example 8is suitable to a variety of end uses, the six-layer film of Example 8 isespecially suited to use in the packaging of processed meat, especiallymeat emulsions and sausage, which is frequently packaged in a shirredcasing, as is known to those of skill in the art. For example, U.S. Pat.No. 4,044,426, to Kupcikevicius, et. al., which is hereby incorporatedby reference thereto, in its entirety, describes apparatus and methodfor stuffing viscous food products into a shirred tubular casingarticle. Numerous other documents describe shirred casings, processesfor their use, and packaged products using same, including: U.S. Pat.No. 3,553,768, to WILMSEN; U.S. Pat. No. 3,798,302, to KOSTNER, et. al.;and U.S. Pat. No. 4,558,488, to MARTINEK, each of which is herebyincorporated by reference thereto, in its entirety.

A casing is produced from the above-described six-layer film accordingto Example 8, by processing resized sheeting to allow for the requiredcasing circumference and lap seal (side of the film) overlap. Byheat-sealing the film to itself, a tube is produced, which can beshirred and later stuffed with a processed meat emulsion. The interiorsurface of the tube is the ionomer-containing layer, i.e., Layer #1, asdesignated in the table immediately above.

Ionomer is known to provide meat-adhesion for cook-in products such asham emulsion, turkey emulsion, and chicken emulsion, which are used inthe production of, for example, the respective products of cooked hamand pressed ham, turkey roll and chicken roll, and luncheon meats.

A shirred casing strand is inserted onto a stuffing horn, with thesealed or clipped end at the exit orifice of the stuffing horn. Thecasing is fed through a brake hole through which the meat mixture isthen pumped. This mechanism allows the meat mixture to be pumped intothe casing at a controlled pressure (i.e., the hydrostatic pressuredeveloped by the elastic memory of the stretched casing).

Additionally, a homogeneous ethylene/alpha-olefin copolymer, such asEXACT 3027 ™ homogeneous ethylene/alpha-olefin copolymer, obtainablefrom the Exxon Chemical Company, can be used alone in Layer #6, andstill provide sufficient seal strength to survive shirring, stuffingwith meat product, and cook-in. The reduced seal strength relative tothe use of ionomer as the outer sealing layer (i.e., a seal strengthreduction of from about 8 to 10 lb/in, to about 4 to 6 lbs/in) may allowthe product handlers the advantage of removing the casing by peeling thecasing open at the lap seal, rather than cutting the casing open withknives and/or scissors.

FIGS. 22-29, together with TABLE XI, provide comparative resultsillustrating the performance characteristics of seals produced accordingto the present invention in comparison with seals using films not inaccordance with the present invention. The comparative results indicatethat seals made according to the present invention can be assubstantially as strong as ionomer to ionomer seals of films not inaccordance with the present invention.

However, some of the comparative results indicate a less than optimalsealing performance of seals produced according to the presentinvention. It is believed that this less than optimal performance couldbe improved upon by merely increasing the level of the second componentin the composition.

Excellent sealing results are apparent, for example, in FIGS. 27, 28,and 29, in which a multilayer film having a thin, 100% ionomer outersealant layer backed up by a relatively thick layer comprising thecomposition comprising the first and second components, was sealed to afilm having a 100% ionomer outer sealant layer. TABLE XI IDENTITY OFRESIN USED IN FILMS OF FIGS. 22 THROUGH 29 1ST 2ND 3RD SEAL RESIN WGT %RESIN WGT % RESIN WGT % KEY EXXACT 3027 100 A EXXACT 3027 100 A EXXACT3027 100 A EXXACT 3027 100 A EXXACT 3027 100 A ESCORENE ECD301 55 TAFMERP0480 35 ESCORENE LD200.48 10 B ESCORENE ECD301 55 TAFMER P0480 35ESCORENE LD200.48 10 B ESCORENE ECD301 55 TAFMER P0480 35 ESCORENELD200.48 10 B ESCORENE ECD301 55 TAFMER P0480 35 ESCORENE LD200.48 10 BESCORENE ECD301 55 TAFMER P0480 35 ESCORENE LD200.48 10 B DOWLEX 2244A100 C DOWLEX 2244A 100 C DOWLEX 2244A 100 C SURLYN 1601 100 (LAMINATION)D SURLYN 1705 100 E SURLYN 1650 100 F EXACT SLP9042 75 TAFMER P0480 25 GEXACT SLP9042 75 TAFMER P0480 25 G EXACT SLP9042 75 TAFMER P0480 25 GEXACT SLP9042 75 TAFMER P0480 25 G CAP OF SURLYN 1650 100 H CAP OFSURLYN 1650 100 H CAP OF SURLYN 1650 100 H CAP OF SURLYN 1650 100 HEXXACT 3027 75 TAFMER P0480 25 I EXXACT 3027 75 TAFMER P0480 25 I EXXACT3027 75 TAFMER P0480 25 I EXXACT 3027 75 TAFMER P0480 25 I

Although the present invention has been described with reference toparticular means, materials, and embodiments, it should be noted thatthe invention is not to be limited to the particulars disclosed, andextends to all equivalents within the scope of the claims.

1-15. (canceled)
 16. A package comprising a seal of a first outer filmlayer to a second outer film layer, the first outer film layercomprising a composition comprising: (A) a first component comprising atleast one member selected from the group consisting of ethylene vinylacetate copolymer, and ethylene/acrylate copolymer; and (B) a secondcomponent comprising at least one member selected from the groupconsisting of elastomer, homogeneous ethylene/alpha-olefin copolymerhaving a density of from about 0.86 to 0.91 g/cc, carboxyl-modifiedpolyethylene; and wherein the first component is chemically differentfrom the second component, and the second outer film layer comprising atleast one member selected from the group consisting of ionomer,ethylene/acid copolymer, and ethylene/acrylate copolymer.
 17. Thepackage according to claim 16, wherein the first outer film layercomprises an ethylene/vinyl acetate copolymer having a vinyl acetatecontent of from about 1 percent to 26 percent.
 18. The package accordingto claim 17, wherein the composition in the first outer layer comprisesfrom about 20 to 70 weight percent of the first component with fromabout 80 to 30 weight percent of the second component. 19-39. (canceled)40. A package comprising a seal of a first region of a first outer filmlayer to a second region of a second outer film layer, wherein the firstouter film layer comprises a homogeneous ethylene/alpha-olefincopolymer, and the second outer film layer comprises at least one memberselected from the group consisting of ionomer, ethylene/acid copolymer,carboxyl-modified polyethylene, wherein the seal has a strength of atleast 2 lb/in.
 41. The package according to claim 40, wherein thehomogeneous ethylene alpha-olefin copolymer has a density of from about0.86 to 0.93 g/cc.
 42. The package according to claim 40, wherein thehomogeneous ethylene alpha-olefin copolymer has a density of from about0.86 to 0.91 g/cc.
 43. The package according to claim 40, wherein thehomogeneous ethylene alpha-olefin copolymer has a density of from about0.86 to 0.905 g/cc.
 44. The package according to claim 40, wherein theseal has a strength of from about 2 to 10 lb/in.
 45. The packageaccording to claim 44, wherein the seal has a strength of from about 3to 10 lb/in.
 46. A multilayer film comprising: (A) an outer layercomprising: (i) a first component comprising at least one memberselected from the group consisting of polyethylene homopolymer,ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, andethylene/acrylate copolymer; and (ii) a second component comprising atleast one member selected from the group consisting of elastomer,homogeneous ethylene/alpha-olefin copolymer having a density of fromabout 0.86 to 0.91 g/cc, and carboxyl-modified polyethylene; (B) asecond layer, the second layer being an oxygen-barrier layer; (C) athird layer, the third layer being a tie layer between the second layerand the first layer; (D) a fourth layer, the third layer being athermoforming, abuse, and ultraviolet-protection layer between thesecond layer and the third layer; (E) a fifth layer, the fifth layerbeing a thermoforming, abuse, and heat-resistant outer layer; (F) asixth layer, the sixth layer being a thermoforming, abuse, andultraviolet-protection layer between the fifth layer and the secondlayer; (G) a seventh layer, the seventh layer being a tie layer betweenthe fifth layer and the sixth layer.
 47. (canceled)
 48. (canceled)
 49. Amultilayer film comprising: (A) a first layer, the first layer being anouter sealant layer, the outer sealant layer comprising a firstcomposition, the first composition comprising: (i) a first componentcomprising at least one member selected from the group consisting ofpolyethylene homopolymer, ethylene/alpha-olefin copolymer,ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer; and(ii) a second component comprising at least one member selected from thegroup consisting of elastomer, homogeneous ethylene/alpha-olefincopolymer having a density of from about 0.86 to 0.91 g/cc, andcarboxyl-modified polyethylene; and (B) a second layer, the second layercomprising a second composition, the second composition comprising:(iii) a third component comprising at least one member selected from thegroup consisting of polyethylene homopolymer, ethylene/alpha-olefincopolymer, ethylene/vinyl acetate copolymer, and ethylene/acrylatecopolymer; and (iv) a fourth component comprising at least one memberselected from the group consisting of elastomer, homogeneousethylene/alpha-olefin copolymer having a density of from about 0.86 to0.91 g/cc, ionomer, and carboxyl-modified polyethylene; wherein thefirst composition is different from the second composition.
 50. Themultilayer film according to claim 49, further comprising a third layer,the third layer being an outer bulk layer, the third layer comprising atleast one member selected from the group consisting of low densitypolyethylene, linear low density polyethylene, polypropylene copolymer,and ethylene/vinyl acetate copolymer, the second layer being between thefirst layer and the third layer.
 51. The multilayer film according toclaim 50, wherein the third layer comprises a third composition, thethird composition comprising low density polyethylene and linear lowdensity polyethylene.
 52. The multilayer film according to claim 49,wherein the multilayer film further comprises: a third layer, the thirdlayer being an O₂ barrier layer, the second layer being between thefirst layer and the third layer; a fourth layer, the fourth layer beinga thermoforming and abuse layer, the fourth layer being between thesecond layer and the third layer; a fifth layer, the fifth layer being athermofornaing and abuse layer; a sixth layer, the sixth layer being atie layer, the sixth layer being between the second layer and the fourthlayer; a seventh layer, the seventh layer being an outer layer and beinga heat-resistant and thermoforming layer, the fifth layer being betweenthe third layer and the seventh layer; an eighth layer, the eighth layerbeing a tie layer, the eighth layer being between the fifth layer andthe seventh layer; and an ninth layer, the ninth layer being athermoforming and abuse layer, the ninth layer being between the seventhlayer and the eighth layer.
 53. A multilayer film, comprising: (A) afirst layer, the first layer being a seal-assist layer, the seal-assistlayer comprising a first composition, the first composition comprising:(i) a first component comprising at least one member selected from thegroup consisting of polyethylene homopolymer, ethylene/alpha-olefincopolymer, ethylene/vinyl acetate copolymer, and ethylene/acrylatecopolymer; and (ii) a second component comprising at least one memberselected from the group consisting of elastomer, homogeneousethylene/allpha-olefin copolymer having a density of from about 0.86 to0.91 g/cc, ionomer, and carboxyl-modified polyethylene; and (B) a secondlayer, the second layer being an outer sealant layer, the outer sealantlayer comprising at least one member selected from the group consistingof ionomer, ethylene/acid copolymer, and carboxyl-modified polyethylene.54. The multilayer film according to claim 53, further comprising thirdlayer, the third layer being an outer layer and a bulk layer, the thirdlayer comprising a second composition, the second composition comprisingat least one member selected from the consisting of low densitypolyethylene, linear low density polyethylene, polypropylene copolymer,and ethylene/vinyl acetate copolymer, wherein the first layer is betweenthe second layer and the third layer.
 55. The multilayer film accordingto claim 54, wherein the second composition comprises low densitypolyethylene and linear low density polyethylene.
 56. The multilayerfilm according to claim 53, further comprising: a third layer, the thirdlayer being an outer layer as well as a thermoforming and heat-resistantlayer; and a fourth layer, the fourth layer being a tie layer, thefourth layer being between the first layer and the third layer.
 57. Themultilayer film according to claim 53, further comprising: a thirdlayer, the third layer being an O₂ barrier layer, the first layer beingbetween the second layer and the third layer; a fourth layer, the fourthlayer being a tie layer, the fourth layer being between the first layerand the third layer; a fifth layer, the fifth layer being anthermoforming and abuse layer, the fifth layer being between the thirdlayer and the fourth layer; a sixth layer, the sixth layer being athermoforming and abuse layer, the third layer being between the fifthlayer and the sixth layer; a seventh layer, the seventh layer being anouter layer as well as a heat-resistant and thermoforming layer, thesixth layer being between the third layer and the seventh layer; aneighth layer, the eighth layer being a tie layer, the eighth layer beingbetween the sixth layer and the seventh layer; and a ninth layer, theninth layer being a thermoforming and abuse layer, the ninth layer beingbetween the seventh layer and the eighth layer.
 58. The multilayer filmaccording to claim 53, further comprising: a third layer, the thirdlayer being an 02 barrier layer, the first layer being between thesecond layer and the third layer; a fourth layer, the fourth layer beingan outer layer as well as a thermoforming, abuse, and heat-resistantlayer, the third layer being between the first layer and the fourthlayer; a fifth layer, the fifth layer being a thermoforming, abuse, andultraviolet-protection layer, the fifth layer being between the firstlayer and the third layer; a sixth layer, the sixth layer being athermoforming, abuse, and ultraviolet-protection layer, the sixth layerbeing between the third layer and the fourth layer; a seventh layer, theseventh layer being a tie layer, the seventh layer being between thefirst layer and the fifth layer; and an eighth layer, the eighth layerbeing a tie layer, the eighth layer being between the fourth layer andthe sixth layer.
 59. The multilayer film according to claim 53, furthercomprising: a third layer, the third layer being a tie layer, the firstlayer being between the second layer and the third layer; a fourthlayer, the fourth layer being an outer layer as well as a thermoforming,abuse, and heat-resistant layer, the third layer being between the firstlayer and the fourth layer; a fifth layer, the fifth layer being athermoforming, abuse, and ultraviolet-protection layer, the fifth layerbeing between the first layer and the third layer; a sixth layer, thesixth layer being a thermoforming, abuse, and ultraviolet-protectionlayer, the sixth layer being between the third layer and the fourthlayer; a seventh layer, the seventh layer being a tie layer, the seventhlayer being between the first layer and the fifth layer; and an eighthlayer, the eighth layer being a tie layer, the eighth layer beingbetween the fourth layer and the sixth layer.
 60. A multilayer film,comprising: (A) a first layer, the first layer being an outer sealantlayer as well as a food-contact layer, the first layer comprising atleast one member selected from the group consisting of ionomer,ethylene/acid copolymer, and carboxyl-modified polyethylene; (B) asecond layer, the second layer being an outer layer as well as being anon-food-contact layer; (C) a third layer, the third layer being aseal-assist layer, the third layer being between the first layer and thesecond layer, the third layer comprising a first composition, the firstcomposition comprising: (i) a first component comprising at least onemember selected from the group consisting of polyethylene homopolymer,ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, andethylene/acrylate copolymer; and (ii) a second component comprising atleast one member selected from the group consisting of elastomer,homogeneous ethylene/alpha-olefin copolymer having a density of fromabout 0.86 to 0.91 g/cc, ionomer, and carboxyl-modified polyethylene;(D) a fourth layer, the fourth layer being a memory layer, the fourthlayer being between the second layer and the third layer; (E) a fifthlayer, the fifth layer being a tie layer, the fifth layer being betweenthe third layer and the fourth layer; and (F) a sixth layer, the sixthlayer being a tie layer, the sixth layer being between the second layerand the fourth layer.